GR1 dies from his backstabbing cousin, GB1.
GR2 is wounded by HER cousin as well, but not killed.
Laniel takes 9 damage from three different goblins.
Two scimitars clank against Titus' armor but one finds its way through, causing him 8 damage.
GB3 slays GP3 with a vicious strike.
Rethan takes 3 damage from a lucky swing.
GG1 hacks at the fallen GR1 in a fit of unrepentant anger.
GG2 wounds GB2 in a surprise attack.

Finally, Halleth punches GP3 and GB3 so hard and so fast their bones crunch. His eyes go wide and he looks at his bloodied hands. A maniacal cackle escapes his lips.

(Everyone may go in any order.)

(Was GB4 in melee range of me to start?  If not, use my reaction to attack it with polearm master when it DOES move into range to try to kill it before it can hit me)

AoO if available: Attack: 12 Damage: 13

Rethan's eyes glaze over slightly in surprise as the room erupts into pandemonium, with goblins killing each other as well as fighting the party.  He gives a mental shrug and continues to wade in with his quarterstaff, moving north as goblins continue to die.

Attack: 20 Damage: 9

Extra Attack: 23 Damage: 9

Bonus Attack: 10 Damage: 10 

Preemptive AoO roll if the goblins survive long enough to get another turn and one moves into melee range of me: 17 Damage: 10

It was.

Morph moves forward to get a better view.

Seeing Rethan to his south, and uncontested goblins to his north, Morph send the bear north to attack the goblins.

Raising his rod again, Morph sends out twin beams of eldritch energy at the same group of goblins.

Morph Move: 1 North, 3 East, to stand behind Halleth

Morph Bonus Action: Direct Bear to move up and attack the three goblins just north of Laniel

Morph Action: Cast Eldritch Blast at cluster of goblins, north of Laniel:

Beam 1: Target Goblin Red: Attack: 18 - Damage: 8 force damage.

Beam 2: Target Goblin Blue: Attack: 26 - Damage: 6 force damage.

Bear Move: 2 East, 3 North to engage goblins north of Laniel

Bear Action: Multiattack

Targets in order of priority: Red, Blue, Green

Bite: Target first alive target from list: Attack: 13 - Damage: 7 piercing damage.

Claw: Target second alive target from list: Attack: 12 - Damage: 14 slashing damage.

Atuan and the clone dodge around on either side of Rethan to go in for an attack against one of the remaining goblins on the south side of the room.

Attack: 20 Damage: 16

Titus takes a step back and starts to inhale deeply, a low rumbling starts emulating from him as draconian light night speed forth upon the goblin horde. Titus arcs his lightning across the room, blasting the swath of foes standing to his southeast.

(I think Titus can hit 6 goblins with a 5x30 ft line breath weapon if those 

Morph and Rethan do an excellent job of clearing out the goblins int he south and center part of the room. Bear misses his wily target. Atuan runs to the middle of the room to find no enemies left. (Atuan has only moved so far and can still take an action and/or bonus action). Titus slides up to line up his breath weapon, giving one of the goblins an opening.

Scimitar Attack: 20 Damage: 7

But then the dragonborn unleashes his lightning breath on four goblins. Dex(13) rolls, nearest to farthest from Titus: 3, 19, 19, 11

Damage from the lightning breath: 10 or half on success.

Titus sizzles all four of his targets, in spite of the quick reflexes by two of them. They fall to the ground, lifeless.

Laniel, seeing the goblins slaughtered around him, moves north to engage the last of them.

Quarterstaff Attack: 9 Damage: 8

Quarterstaff Attack: 11 Damage: 12

Kick Attack: 13 Damage: 6

Kick Attack: 9 Damage: 9 (1 Ki)

In a whirlwind of attacks, the first goblin he encounters dodges most of his strikes, only receiving a painful looking kick to the head.

(Atuan can still take an action. )

With a deft twist, he flings a dagger towards one of the few remaining goblins still standing in the room!

(nonlethal declared!) Attack: 23 Damage: 6

At this range it is at disadvantage: 24

 Atuan seems to make a wild throw but it is deadly in its accuracy. The dagger hits the leg of the goblin that Laniel just kicked and it falls to the ground, unconscious.

DM shield:

The last remaining goblin swings at Laniel with her scimitar.

Scimitar Attack: 19 Damage: 8

Halleth marvels at the destruction his fists made, a wild look in his milky eyes. He turns and marches steadfastly away, muttering to himself. "I don't know what happened, but I don't need weapons. I will kill them with my bare hands..."

Laniel cringes as the blade finds its mark. He strikes back with three swift strikes.

Quarterstaff Attack: 22 Damage: 8

Quarterstaff Attack: 17 Damage: 10

Kick Attack: 26 Damage: 8

Laniel continues to struggle in hitting the agile little goblins but his kick does find a soft spot. The goblin falls with a thug. Only a single unconscious goblin remains.

(Combat has ended.)

Morph's expression takes on one a look of mild concern, as he looks over the bodies of the dead goblins.

"It kind of feels wrong."

Morph turns as Halleth marches off with a look of mad glee in his milky eye's.

"Ahh, guys, are we going to continue following this guy? Because he's heading off..."

Morph points in the direction Halleth just headed off in.

Rethan shakes his head, still confused as to what exactly just happens, but gives a sigh at Morph's comment and continues to follow Halleth.

Rethan and Laniel and anyone who joins them:

Titus also gives chase, not wanting to let the undead out of his sight.

Titus, Rethan, and Laniel:

Rethan follows (unless someone gives a reason to do otherwise)