Rust takes two bites, and tries to wriggle free of the Rats, but fails.
//---DM Rust takes 12 damage and remains on the ground ---//

>>> 2nd Round <<<

Brynn tries to move behind the rat that is moving up the stair to hit him with his rapier, which hits the stair railing and he misses it.

//--- DM You miss the attack anyway, but take into account you only can use sneak attacks when you are somehow hidden (sneaked) )

/--- Initiative Rolls / 2nd Round---//
Brynn
Arr --> next
Rats (1) both dead
Coltinar --> on deck
Rylia
Rats (2) One dead /One approaching stairs to try to go up
Paladin
Braxiel
Rats (3) attacking Rust
Rust

Arr notices the predicament of the warforged shopkeeper and hurries to assist against the rats that hold them to the ground. They attack with force, neglecting their own defenses.

free: reckless attack 
action: attack with cleaver: 18 for 9 slashing damage
Bonus action: attack with pipe: 26 for 2 bludgeoning damage 

Brother Coltinar

Action: 

Cast: Toll the Dead  4 if target is at full health.

Cast: Toll the Dead  4 if target is not at health.

Bonus Aciton:

Cast: Healing word  9 on Rust.

Movement to See Rust (upto 30ft), as long as he doesn't take opportunity attack from the Rat near the stairs.

Reaction:

[Reaction]Warding Flare[/Reaction]   Posted here if the link doesn't work.

Warding Flare:  Also at 1st level, you can interpose divine light between yourself and an attacking enemy. When you are attacked by a creature within 30 feet of you that you can see, you can use your reaction to impose disadvantage on the attack roll, causing light to flare before the attacker before it hits or misses. An attacker that can’t be blinded is immune to this feature.

Seeing Rust down and being doubly attacked, Arr rushes to her defense. Without measuring strength and without worrying about his own rear, the barbarian strikes two consecutive blows, managing to defend himself from one of the beasts that feels the blow.
//---DM Arr, Are your dual wield some trait? I couldn't find it.

Coltinar throws magic words at the rat at the edge of the stairs inflicting da amage on him that nearly knocked him over.
The cleric so rushes to help Rust giving her some healing from the light of Dol Arrah.

/--- Initiative Rolls / 2nd Round---//
Brynn
Arr 
Rats (1) both dead
Coltinar 
Rylia --> next
Rats (2) One dead /One approaching stairs to try to go up
Paladin --> on deck
Braxiel
Rats (3) One dead /one attacking Rust
Rust

Still holding her position, Rylia chants out different arcane words this time.  Making a different pattern with her hands she casts Magic Missile targeting just the closest rat. 
(Damage: 3. 3, 5)

(Anyone can dual wield when using light weapons but the bonus attack does not use the ability mod for damage. There’s a fighting style that allows the ability mod for damage and a feat that allows the use of weapons that aren’t light. Arr has neither and uses dual wield at its basic.)

Rylia sees that Rat approaching the stairs, enraged with pain and with a clear intention to attack her, and decides to attack him first. The Rat comes so focused on her that doesn't even notice where the three darts that hit him came from and falls lifeless at the foot of the stairs.

/--- Initiative Rolls / 2nd Round---//
Brynn
Arr 
Rats (1) both dead
Coltinar 
Rylia 
Rats (2) both dead
Paladin --> next
Braxiel --> on deck
Rats (3) One dead /one attacking Rust
Rust

Paladin keeps hitting rats by Rust like he's pounding in nails 

Attack: 12 Damage: 10 

Imbued with his spirit of justice, Paladin uses his ax like a hammer on the last rat that still had a thread of life and makes it fly across the room, falling over some scrolls rolls, and some flasks.

//--- Combat is finished. All rats are dead ---//

"For the light of Silver Flame! Thank you, sir" Rust thanks Paladin. "Thank you all", she says looking at the rest of you. "I don't know what would have happened if you hadn't shown up!" She says as she looks around trying to get up. "Wow! What a mess! These attacks are getting worse every day!" Says the Warforged in a sad and melancholy tone as she looks around at the damage done: a fallen shelf where there were several flasks and pots, scrolls spoiled by poisoned rat blood, broken weapons... a real damage, indeed!

“Glad to help.”Arr says nonchalantly, while he looks over at the fallen shelf trying to determine if he can put it back upright without causing further damage. “But where do they come from? There must be a nest nearby if they attack so regular, or is someone sending them here?”

"Ugh. Rats. Horrid things. It is a pleasure to protect anyone from such a plague." Paladin wipes the rat guts from his hammer and slings it. "Are you hurt?"

Quote from cyreon >>

“Glad to help.”Arr says nonchalantly, while he looks over at the fallen shelf trying to determine if he can put it back upright without causing further damage. “But where do they come from? There must be a nest nearby if they attack so regular, or is someone sending them here?”

 Give me an athletics roll

Bryn sheathes his weapons and gives Rylia a big grin. "Nice shooting, Miss 'I don't think I'm very powerful.'" he says to her playfully.

Bryn looks around at the mess. When Rust mentions regular attacks, he also thinks a nest must be nearby - or perhaps an old passage hidden by new construction? He will investigate the room, checking the walls and floor in particular to see if he can determine where the rats are entering the room. (Investigation: 16)

Arr tries to lift the shelf in an effort to help cleaning up the place (Athletics: 25)

Brother Coltinar chips in with helping clean the place up too while looking about for concerns and learning more about the shop and what it has.

Brother Coltinar Perception:  8

Brother Coltinar Investigation:  2

Brother Coltinar Athletics:  20

Braxiel said will join the rest of the party down stairs now that the fighting is over. He is feeling rather useless with the party achieving great results without him. 

Rylia shakes her head, a grin on her face after Bryn's comment. "Ok, so I do know a couple simple spells!" 

Briefly grasping her blue crystal she casts Dancing Lights summoning 4 bright almost white globes of light to float nearby.  She will look for herself to see if there's any sign of where the rats might come from. 

(Investigation: 10)

"I'll be fine, thanks! They got me a few bites, but luckily, their illness doesn't hit me, as you can imagine," Rust responds to Paladin. "Besides, I think one of your friends helped me. I felt an aura of light giving me some life force, I think that was what helped me to avoid more bites!"

Braxiel goes downstairs and finds the big mess.
Arr lifts the fallen bookcase without difficulty. Coltinar still tries to help then, but when he reaches the shelf it is already up and he ends up helping to pick up the fallen pieces on the floor.

Suddenly, Rylia makes her orbs of light appear and the mess becomes even more evident.

Coltinar sees that this basement has mostly weapons and equipment kits, plus a few shelves with pots and flasks of various sizes, many now broken.
Near the stairs, at the west wall, racks held swords of various sizes, four crossbows, and some arrow cases. On the other side, some daggers.
On the shelf that was raised by Arr, some leather, wooden and glass pots with various stones. One of the broken pots had green scales on it that the Coltinar recognizes as dragon scales.
In the background, to the east, next to where Rust and Paladin are, a shelf with some stacked scrolls and some fallen on the ground under two broken crossbows and where one of the Rats lies.

As the orbs of light illuminate the room, Rust looks around. "Yeah! This place really needed a good cleaning and re-arrangement", says Rust as she moves to pick up the things that have fallen from the shelf where Arr is, in particular the fallen scales on the floor! "Damn!"

Brynn, now with Rylia's help, investigates the place looking for some clue where the rats came from.
After finding some gnawed leather tracks, he notices that a small ventilation grille behind a counter is not fully fixed. He pulls on the grate and it easily comes free. Brynn and Rylia see what looks like a tunnel, not very wide but big enough for a medium creature to squeeze through. They notice crumbs which raise the suspicion that this is where the Rats came from, even though, strangely, the grate was leaning into place as if it were closed.

Paladin sees them eyeing the grate. "Rust, I understand it might be hard to tell: do you see anything missing? Rats don't close the door behind themselves. But a thief looking to cover their tracks might." 

Rylia, seeing the grate Brym discovered, nods in agreement with Paladin. "It does seem that someone might have used the rats as a distraction to get away." She hesitates a moment though as she recalls being attacked last night and so easily overcome. "Um, perhaps you shuold have someone check that out."