oh I gotcha, yeah I'll do that

The rat in front of you drops dead, pierced by Peter's arrow, which leaves just the two rats at the back of the room hidden from view by mounds of rubble which count as total cover for the purposes of targeting attacks.

It's Muirgurn's turn, and Razil, for the time being, neither of the living rats can be targeted with your spell and you are free to revise your action.

Muirgurn will call down sacred flame to smite one of the skulking rodents (R4, DC13 save or 7 radiant damage), since mounds of rubble are no protection against Moradin's divine power - albeit diluted in Muirgurn's inexpert wielding.

The rat tries to avoid the radiant flames descending on its hiding spot. 11

... but to no avail. You can hear it give a dying shriek from the far side of the room and it expires.

The last remaining rat continues to hide behind the rubble, cowering in fear, so unless Razil would like to do something combat-related, I think this combat encounter is pretty much over. And assuming that’s the case, what would you all like to do?

Muirgurn has no particular regard for such beasties, so if he is aware of it, would most likely exterminate it like its brethren.

In any case, assuming the rodent threat is neutralised, he will press on with the exploration.

Peter would keep cover on anyone who went to exterminate the final rat, and then agree to going left, picking his glowing coin back up from the floor. He'll remain in the back

Another casting or two of sacred flame ensures the final rat is consumed by radiance.

After traversing the debris and refuse scattered about the room, you find the door to the left easy to open. Beyond it is a short ten-foot long hallway that ends in another door.

Picking up your glowing coin, Peter, you notice that towards the back of the room, in the rats' nest, is a mass of old bones, chewed leather straps, and bits of armor.

"Hold up a second fellas, let's see if our furry friends found anything fun". after saying that peter makes his way over to the pile and rummages through it

If Raz could use his movement to get in viewing range of the rat he would do so, otherwise he would prepare to fire off a blast as soon as it came in sight

Muirgurn will listen at the door whilst Peter searches.

Making you way over to where you can see the last rat, Razil, you can confirm that it is dead.

Listening intently at the door at the end of the short hallway, Muirgurn, you hear no sound coming from the space beyond.

Meanwhile, Aldrich retrieves one of the arrows he shot. The other that killed one of the rats broke when the rat rolled over dead.

It takes about ten minutes to carefully search through the pile in the rats' nest. 5

After searching, Peter, you come up with a belt attached to which is a silver dagger in a sheath and a bag containing 30 electrum pieces.

((hey this has been confusing me, in 5e is electrum between gold and silver??))

Peter will toss a quick glance back to his companions, and if he appears to be relatively unseen he'll try to slip 10 of the electrum pieces out of the bag and into his purse. after that he'll turn back to the group "I found some electrum, and this dagger here", he'll toss the dagger to Razil, "make anything of that??"

Yes, 1 electrum piece is worth 1/2 gold piece or 5 silver pieces. It tends to be an older form of currency minted by ancient civilizations and not much used today. I made a typo, though. It’s actually 30 ep in the bag, and I’ll leave it up to the other players whether they saw you pocket 1/3 of the coins and what if anything they do about it. 

oh if there was only 30 and they were worth 5 sp i wouldn't have pocketed any, but maybe they saw me contemplate it

Raz peers quizzically at Peter for a moment, but quickly turns his attention to the dagger. Using one of the dead rats as a target, he takes a few swings to get a feel for the balance and sharpness. Afterwards, he'll inspect it a bit closer to see if he gets any magical sense from it.