With or without the torch, depending on our contested check.

Alright contested STR check to see if Elero can wrestle the torch from Mark:

Elero: 3

Mark: 18

Mark easily pushes Elero away. Far meaner and tougher than Mark has ever been before.

"Dammit, snap out of it," Elero says, frustrated.  He turns to Erix. "That troll will kill us all if he wakes it.  Help me."

Erix wonders what he can do and speaks quickly . "although, I do think we can kill the troll. Getting mark out if this is important. How do you think we can do this? Lesser restoration isn't gonna do much I guess. Maybe we can try to knock him out, and see if sleep does him well?"

He at least orders the animals to walk in front of Mark and slow him down. 

Adding a 4th to the bunch (final one from bag for the day) 7: dire wolf

Mark continues to walk but says, "We must cleanse this space, we must make it clean. There can not be life in such a holy ground. Help me achieve this and great things will come to you, to us!" 

"Is it just the troll, or are there other beings that need to die?  If we're there, are you going to try to kill us next?" Elero asks Mark, while also trying to get in his way and slow him down.

Elero will glance at Erix. "Knocking him out might be our best bet, but that might also make him attack us."

Mark begins to pick up speed and says, "I would never hurt you, for you are one of the sanctified. But if you stop me, the cleansing will come for you too!"

Well it's up to Erix and Elero still. Mark is about to enter the room with the Troll.

Looks like we're fighting a troll.  If this is really going to happen, Elero's going to expend that spell slot to convert the Protector Cannon into the Flamethrower Cannon.

"I guess our best bet is to fight the troll, and help Mark win."

OK, so you'll all get as much time as you need to prepare, and all get a round of actions while the Troll is prone to do whatever. Then it's the Trolls turn:

Group 1: You all

Group 2: Troll

You enter the moss room again where the Troll is sleeping quietly. You all are up.

Clumulk: (8,11)->11 for 5+1dmg
Boar: (3,10)->10 for 5+4dmg
Dire wolf: (10,7)->10 for 10+6dmg
Land beast: crit(26) for 8+5dmg

Erix himself cast Thorn whip: (9,18)->18 for 5+4dmg

Elero will keep at a distance, firing his crossbow at the troll (which I think is at disadvantage since it's prone, and I think all the melee attacks are at advantage.  DM, you can tell us for sure):

Crossbow attack: 22 or 16 to hit and 8 damage

The newly-modified tiny metal dragon will approach the troll to keep the animals out of its cone of fire and unleash its flame weapon:

9 damage, or half that on a DC 13 Dex Save 

Mark will look up as if listening to a voice then back at the troll and tries to burn the surrounding moss and throughs alcholal onto it from a flask he has in his coat pocket. Then he slash at the beast with his rapier, right through the neck. 

Attack w/adv: 15

Damage w/ sneak attack: 7 + 2 = 9 

He will then move back from the roaring flames and with a maniacal style start to laugh. 

Troll DC 13 DEX Save: 18

The moss catches on fire and the floor and walls of the room start to go up in flame.

The Troll itself is also lightly aflame, preventing the moss from regrowing over its wounds. It stands up and tries to Rend with it's jaws and hands. First trying to hit the Land Beast, then the Boar, then the Dire Wolf:

Rend 1 Attack: 18 Damage: 12 Slashing

Rend 1 Attack: 16 Damage: 15 Slashing

Rend 1 Attack: 8 Damage: 14 Slashing

You all are up. The Troll is surrounded by Erix' animals and it thrashing wildly.

Does it seem like we'll get burned up if we stay in this room, or is the moss just burning away, and the rest of it is stone, and eventually that fire will go out on its own?

In the meantime, Elero will take another shot with his crossbow, and the Eldritch Cannon will "flame on" again.

Crossbow attack: 13 to hit and 10 damage

Eldritch flame: 6 damage or half that on a DC 13 Dex save.

Also, how injured does the troll appear after all of that?

The moss itself seems to be burning, once it's gone the room will be safe. 

Troll DC 13 DEX Save: 20

Even after your assault, the Troll seems hurt but still surviving.