Kei instantly seals up the pit, trapping the two constructs below. For a brief moment there is silence, and then the banging begins. Huge clangs and tremors as the constructs beat at the door mercilessly from below. But it holds, for now.

Peri:

Peri's ears ring from Boko's thunderous blasts. He peeks around the corner and sees neither construct, though he can hear them sorting themselves out in the bottom of the pit.  He readies an eldritch blast for the moment a head appears above the lip of the pit, but then Kei produces a door from nowhere and seals the statues in. 

"Well done, everyone! All still standing, I see, so I'd call that --" And then the banging starts, the statues trying to batter their way through the new door. "How long can that hold those things?" he asks, rummaging though his pack. He pulls out two flasks of oil. "Aha! I knew they come in useful some day!" He hurries to the other side of the trapdoor and looks for a gap to pour the oil through.

Dwal looks on amazed.

"That worked out better than any plan I had." he says. "Alright, no what? Do we retreat or move on?" he asks. 

Gerrard:

"We should probably wait to see if they can break out, or if Master Fenwader has a plan to neutralize them," responds Gerrard.  "If the room they were in can be made secure once we finish dealing with its guardians, we could recover a bit there while we search through the items stored there," he suggests.

Bang! Bang! Bang! Bang!
Four enormous impacts can be heard on the underside of the iron door.

Attack: 12  Hit: 8 damage
Attack: 19  Hit: 10 damage
Attack: 15  Hit: 12 damage
Attack: 23  Hit: 13 damage

...none of them seem to compromise the integrity of Kei's door, at least from what you can see from this side.

A grinning specter appears suddenly from the north (beyond the acid pit) and tries to tag Kei from behind before retreating to the north again.
Life Drain Attack: 13   Hit: 13 necrotic damage (and Kei must succeed on a DC 10 Constitution saving throw or his hit point maximum is reduced by an amount equal to the damage taken.)

Kei and Boko may have an opportunity attack against it as it flees north.

Gerrard:

"I was rather hoping they wouldn't be tall enough to reach the door at the top of the pit with their weapons," says Gerrard, as he waits for Peri to do his work and perhaps others to come up with something else brilliant...For his part, Gerrard stays at the ready, poised to stab at any foes who make an appearance--even if it is through a wall...

Readied Attacks when needed:

"If'n ya can't find a space ta pour that oil in" Dwal says, "Ya might want ta try ta put it all along tha front of tha pit so if'n they get through tha door, it might give them a it of trouble climbing out. An' we can add to that trouble but making sure they don't climb out."
Dwal pauses.
"An' if ya have enough, we can make sure they are coated in it 'afore they climb out. We can keep 'em slick and set tha oil on fire ta see if we can help melt 'em".

These are the only suggestions that comes to Dwal's mind. 

Kei 

Oblivious to the approach of the ghostly figure, Kei is quite shocked by the near miss of the spectres attack. "Whoa!" He instinctively steps away from the ghosts position and ends up on the other side of Boko. "Seems we have another problem" he points in the direction of the retreating enemy.

((Unfortunately, without a weapon in hand he can't attack the fleeing foe. No AoO for the doorman))

Peri:

Peri carefully pours the oil through the narrow gap. "I was plannin' on pourin' it on the walls, but Kei's hatch was even better. Can't really get to the walls now, unless we open the hatch, and that seems like a poor choice!" He finishes emptying the two flasks and backs away to the south side of the pit, taking up his spear again. "Now, if we only had a way of lightin' this oven..."

"I got that covered." Dwal says. "Though in such an enclosed area, if tha heat gets hot enough there may be an explosion that pops the lid off." 

Once ready and everyone steps back and noone opposes the idea, Dwal will step back and cast Prestidigitation and light the oil. Then Dwal will use Control Flames and increase the intensity of the flames as best he can. 

Gerrard:

Backing off as suggested but still keeping his guard up, Gerrard comments to Dwal, “We do seem to work well, together, don’t you think Brother Fiercehammer?  I’d rather you stay with us for the long term if you would, but I respect your decision either way.”

Moving and renewing the ready action should enemies pop out from walls or pits with doors…

Boko unarmed AoO : 21 Damage: 6

She also quirks an eyebrow at the pair by the oven, snaps her fingers, and manifests a flaming sphere inside the pit. 4 fire damage on the first round on a failed DEX15 save...

Boko manages to tear the specter to shreds of cold vapor with a well-placed swing of her tattooed arm. It has been dispatched to whatever realm such entities are sent to. That specter is no more.

Gerrard readies himself at the edge of the pit in case the iron men emerge.

Peri pours oil through the seam in Kei's iron trap door. Dwal ignites the unseen oil below, expanding the flames to fill the pit. (PHB: Burning oil causes 5 fire damage per turn.)

Boko one-ups them both by conjuring a massive ball of pure flame, below. 
DC 15 Dex Saves: 22 and 16

Kei may still act.

Peri:

After Boko punches a ghost back to death, she makes some sort of arcane gesture and the oven that he and Dwal had created turns into a smelter. "Oho! The more I see, the more I like her! You did some top-notch recruitin' in Seaton, Lord Feldren -- much better than the last one you scaped up," he says with head nod toward Kei. "Though I suppose he does come in handy from time to time, like when you need a lid for your kettle and such. You think we can brace the ladder against the hatch to keep 'em from batterin' their way out?"

((Peri will help get the ladder into position using his mage hand so that no one gets burned.))

Gerrard:

"Indeed, our companions are quite capable, Master Fenwader, even our erstwhile captain," responds Gerrard with a wry smile.  Sheathing his off-hand weapon, he helps Peri with the ladder.

The ladder in place, four more thunderous impacts can be heard on the underside of the iron door. 

Attack: 22 Hit: 12 damage.
Attack: 17 Hit: 11 damage.
Attack: 24 Hit: 10 damage.
Attack: 20 Hit: 10 damage.

There is no apparent damage to the new trap door. 
Everyone may act (or wait and watch.)

Dwal will just wait. Boko's spell does more than his attempts so he will take a back seat and wait and see what happens.

Peri readies an eldritch blast in case the statues break out.
(EB #1: 18 for 7; EB #2: 8 for 9 -- just to keep things rolling if they do manage to get loose.)

Gerrard:

Continuing to stand on one end of the ladder, Gerrard stays at the ready with his glowing rapier in case the other escaped specter or the foes in the pit below make an appearance.