(edited to add damage narration)

Daphyra makes a short squeaking noise as the Eye looks at her, and recovers, looking worn. She doubles over as the redbrand's crossbow bolt hits her in the side, drawing blood from her soft fur.

Daphyra points at Redbrand 5 and calls “Dong’”, casting Toll the Dead. She retreats to K8 for some cover. 

movement - k8

action - toll the dead (dc13 wis or 8 damage if unhurt, 1 if already hurt) 

bonus action - none

(THP available for this round = 4)

Round 4 Results (partial)

Another foe falls to Marten’s marksmanship as his arrow impales Redbrand 5 through the chest. The man throws up his crossbow reflexively, but dies an instant later, simply crumpling against a wall. Marten is unable to Hide in the wide open doorway at J3, however, he no longer has line of sight with the enemies remaining in the room.

Nosam holds in place.

Daphyra’s Toll the Dead rings in Redbrand 6’s ears since R5 is dead. The Redbrand mostly fights it off, taking 1HP damage.

Those near the stairs at E13 see a sudden rush of matted hair and muscle, then a shout of surprise, followed by THUMP, THUMP, THUMP, “Owiieeee!!,” as a large figure falls prey to Berry’s Home Alone tactics. A sound of many feet comes from downstairs.

You are now situated like so:

Berry, Kiselina and Vidruth may now act in any order.

“Hold if you can, Nosam! Sounds like there are still many of them! Throw the bodies down, perhaps it makes it harder for them to come up?” Replies Berry to Nosam. “Any ideas how else we can block the stairways? Crates?” Berry brandishes his scimitar and lashes out at the last remaining redbrand in the main chamber (hit: 22 for 9 damage).

"toss things down at them" vidruth says tersely "ive got more ball bearings too. ill roll them when ive got a minute" vidruth walks to the top of the stairs "daphyra, if you can summon water, now is the time" he pours his waterskin down the stairs, freezing it as it goes to make the top of the stairs as slippery as possible, then steps aside out of site

move: to 13, actions, then to f12

free interact: pour out waterskin

action: shape water, freeze

Kiselina hears the commotion down the stairs that he’s been vigilantly guarding and considers going back to ‘throw something’ (like his breath weapon) down on as many combatants that decide to sally forth up the stairs. But after seeing Daphyra succumb to One-eye’s gaze, he decides to continue on his course of action. Plus, Nosam and Vidruth seem to have it handled.

He watched as two crossbow bolts flew out of the passage to the northwest, he decides to try and engage those that launched them. He’s anxious to get Glassstaff as soon as possible as well, figuring the wizard holds information that would be useful to the group (about the Black Spider).

He cautiously steps into the opening where he finds a Redbrand’s body and another still standing. He’s a little startled even as he was prepared, he makes an attack against the combatant, then shuffles back out of the opening.

“One Redbrand down, one still stands!”“Mistress, can you manage to hold out a little longer?”

Move: H6 to attack, end at H7  
Action: Attack R6 (10’ reach) To hit: 10, Damage: 4  
Bless countdown: 7

Round 4 Results (final)

Vidruth adds any icy coating to the stairs at D13.

Kiselina slashes at Redbrand 6 but misses.

Berry strikes the Redbrand he hit before, slashing across the man’s abdomen and cleaving through his boiled leather armor to leave a deep gash. The man staggers, his eyes dilated in fear.

That Redbrand (R3) disengages, and flees for his life down the hallway at L14 and ends the round out of view.

At that moment, the secret door Marten had found at M1 swings open, and Redbrand 4, who had disappeared down the south tunnel several rounds ago, now enters the fray, leading another band of Redbrands bearing weapons. Seeing Marten trying to hide from the occupants of the cavern chamber, they quickly surround him, unleashing a fury of blows.

Now a tumult erupts from the tunnel Kiselina is guarding. The Redbrand near him strikes at Kiselina then leaps across the chasm, risking an Attack of Opportunity from the paladin. If he is not struck down, he approaches Daphyra with weapon drawn.

Three more Redbrands follow him, two leaping across the chasm after attacking Kiselina, and one leaping onto the bridge before engaging Kiselina from behind.

Two bugbears follow them up the same tunnel and lay into the paladin with morning stars.

Redbrand 4 attacks Marten (13 / 5 piercing, 19 / 6 piercing)

Redbrand 7 attacks Marten (11 / 6 piercing, 14 / 6 piercing)

Redbrand 8 attacks Marten (23 / 4 piercing, 8 / 4 piercing)

Redbrand 9 attacks Marten (24 / 6 piercing, 15 / 5 piercing)

Redbrand 10 attacks Marten (17 / 7 piercing, 20 / 5 piercing)

Redbrand 11 attacks Marten (13 / 8 piercing, 21 / 3 piercing)

Redbrand 6 attacks Kiselina (20 / 4 piercing, 19 / 4 piercing)

Redbrand 13 attacks Kiselina (20 / 6 piercing, 18 / 6 piercing)

Redbrand 14 attacks Kiselina (16 / 8 piercing, 7 / 3 piercing)

Redbrand 15 attacks Kiselina (16 / 3 piercing, 17 / 3 piercing)

Bugbear 2 attacks Kiselina (19 / 4 piercing, 15 / 7 piercing)

Bugbear 3 attacks Kiselina (12 / 4 piercing, 9 / 7 piercing)

N.B.: If Marten or Kiselina are down, any further attacks will not be made against them. Instead, the remaining Redbrands will hold in place.

You are now situated like so:

Kiselina, please take AoO at Redbrand 6 after he attacks but before he leaps away, and before suffering attacks from the remaining foes.

Daphyra, Marten, and Nosam may then take Round 5 actions in any order.

Marten: Round 5

A nagging feeling had been tugging at the back of Marten's mind since the start of the fight.  He remembered seeing four Redbrands with the bugbear, but he could only account for three of them.  He hoped that the fourth Redbrand had simply fled, but he was starting to worry that the man had run to fetch reinforcements.  If they could just get the whole party together behind a narrow bottleneck where Nosam or Kiselina could block the way, they could hold off a larger group of Redbrands while the rest of the party tried to pick off their opponents from a distance.

Unfortunately, Marten had expected the reinforcements to arrive from the southeast tunnel, not the secret "treasure room" that he assumed was behind the secret door he had found.  Therefore, he was startled when that secret door swung open, and a whole troop of Redbrands emerged!  As the brutes surround him, Marten tries to dodge, but there are too many of them.  There seem to be swords stabbing at him from every side, and he quickly succumbs to the attack and loses consciousness.

Unconscious

Death Save 1: 10

Redbrand 6 stabs at the Paladin with his main hand and misses. Maybe it was the angle of the attack. But he adjusts for the off-hand attack and finds its mark, piercing through his armor. 
As the cloaked figure leaps away however, the knight is able to swing his halberd and catch the back of him with a slash. 

(Reaction) Attack of Opportunity: To hit: 24, damage: 6 slashing

Nosam sees the commotion and makes a dash to get near Kiselina to offer support, possibly cover the bridge to avoid K being attacked from both sides. 

Movement and Action- Dash to H7 or H8, ready to hopefully attack R13 and cover bridge next round

Daphyra sees the Redbrand6 heading towards her, points at him and says "Dong!" (Toll the Dead for 10HP necrotic, as he is already damaged). She calls back to Vidruth, "Can't do that, I'm afraid..." and uses her final spell slot to call "Heal!" to Marten healing him for 4 HP. She then retreats back to K14, risking an AoO if R6 is still alive.

(THP from Twilight Sanctuary is 3 for this round.)

Action: Toll the Dead (DC13 Wis or 10 necrotic)

Bonus action : Healing Word for 4HP

Movement: to K14

Corrected Bugbear attacks vs. Kiselina: 

Bugbear 2 attacks Kiselina (16 / 15 piercing)

Bugbear 3 attacks Kiselina (20 / 15 piercing)

Quote from kohlmetz_d >>

Redbrand 6 stabs at the Paladin with his main hand and misses. Maybe it was the angle of the attack. But he adjusts for the off-hand attack and finds its mark, piercing through his armor. 
As the cloaked figure leaps away however, the knight is able to swing his halberd and catch the back of him with a slash. 

(Reaction) Attack of Opportunity: To hit: 24, damage: 6 slashing

 The Redbrand survives Kiselina’s reaction and now faces off with Daphyra.

Round 5 Results (partial)

Nosam runs to H8. This takes only 25’ of movement, so he may now attack R13 as part of his round 5 turn.

Daphyra’s Toll the Dead has no effect on the approaching Redbrand 6, who takes advantage of the harengon’s retreat to lunge at her from behind (AOO 7 / 8 piercing), before she moves away to K14.

My mistake: the bugbears should have gone at this time in initiative order. 

Nosam may attack R13. Additionally, Berry, Kiselina and Vidruth may now act in any order.

The sudden rush of the redbrands upended their endeavour quite effectively. Berry stares stupefied when a never-ending flow of them just stepped out of the walls in the storage rooms, he almost didn't notice how his own adversary, R3, got away. Then they fell Marten. Then, two bugbears overwhelmed Kiselina. And Daphyra stumbled with her retreat. The odds couldn't be worse, but a fire ignites in Berry in these few seconds in which everything fell apart. He loosened his shield somewhat and then rushed over Daphyra to confront the bandits (J7 if possible). He readies to throw his shield when he believes that most foes, who would, did attack him and lets himself slip into a rage.

Move to J7
Action: ready to throw his shield (improvised weapon) after a couple of redbrands attacked him (ideally just before he takes his next turn)
Bonus: enter rage

(Daphyra is down from the AoO)

"friends" vidruth says darkly "its been good running with you" he runs up behind nosam and launches a bolt of flame at a redbrand (r13, unless they died in which r14)

move: g9

action: cast firebolt (15 to hit 9 damage)

he growls in orcish as he sees his allies fall around him

Kiselina managed to catch Redbrand 6 as he moved past like lightning, but it wasn’t enough to end its life. Then the surprise, a stream of fellow Redbrands follow suit.

They barely slow down to leap across the chasm, but manage to take alternating stabs at the knight as they pass. His armor is only marginally protective, and his movements seem ill timed with the apparent coordinated attacks of the thugs. A strike here in his thigh, a miss there. Gaining some sense of the rhythm another miss, but the combatant quickly adjusts in the second before his jump and lands an impressive stab through his armor into his chest. This cause the Dragonborn to spit up blood. Steadying himself, another miss, followed quickly with what would normally be a minor hit to his forearm.

Exhausted by the relentless attacks, the Paladin manages a second of reprieve. “Violence of action, this is what it looks like.” His last thought before the morning star from a bugbear slams into him, knocking him to the ground assuredly cracking his skull. As his vision blurs, he sees the feet of another…or is it just his eyesight. He may never know.

The effects of the Bless spell ends

Death Saving throw: 1, two failures!

Nosam gets to R13 without any major issue, winds up, and unleashes a massive swing of his hammer. 

Attack on R13- Hit 21 (16+5), Damage 9 (6+3)

ooc: unsure if there was still an extra D4 bonus to hit from the buff, if so it would be another +3

Quote from cyreon >>

The sudden rush of the redbrands upended their endeavour quite effectively. Berry stares stupefied when a never-ending flow of them just stepped out of the walls in the storage rooms, he almost didn't notice how his own adversary, R3, got away. Then they fell Marten. Then, two bugbears overwhelmed Kiselina. And Daphyra stumbled with her retreat. The odds couldn't be worse, but a fire ignites in Berry in these few seconds in which everything fell apart. He loosened his shield somewhat and then rushed over Daphyra to confront the bandits (J7 if possible). He readies to throw his shield when he believes that most foes, who would, did attack him and lets himself slip into a rage.

Move to J7
Action: ready to throw his shield (improvised weapon) after a couple of redbrands attacked him (ideally just before he takes his next turn)
Bonus: enter rage

Redbrand 6 does indeed run at Berry, short sword jabbing at the fairy. Berry’s readied attack is triggered.