Gerrard:

Agreeing with Peri but not liking it, Gerrard grates his teeth at the suffering of the innocent creature and waits.

A full hour passes before things finally go silent. Spying ahead, Boko relays that the torturing guards finally appear to have left the room. From the sounds she can hear, the locathah is back in his cell (somewhere to the west end of the set of doors), still whimpering in pain.

Peri:

The hour of waiting had moved as slowly as a becalmed galleon under tow. He had moved nearer the outside entrance of the tunnel to limit his hearing, but the shrieks that carried that far set his teeth on edge. By the time he noticed the cries had ceased he was a topsail in a hurricane, ready to burst. It hardly felt like any vindication when Boko had confirmed that the guards had left. He could tell by his companions' haggard faces the wait hadn't been any easier for them. He did feel an extra measure of guilt that it had been his insistence that had stayed the others from putting an end to the poor creature's suffering. In grim silence he began rigging the block and tackle to heave the serpent's coils nearest the door out of the way, accepting the repulsive feel and gagging smell as some degree of penance. Not that it will make it better  for the locathah...

Gerrard:

The young noble helps with the block and tackle as best he can, asking, “Captain Fenwader, are you planning to rig this so the eel body can be put back into place when we are done?”

Kei 

By the time the guards finish their interrogation even Kei's blood is boiling. He'd seen and heard people being tortured before, whether it be at the hands of guards or less savoury figures, but never had it lasted so long. He assists Peri where he can with rope work. Damn. He curses his lack of foresight. The one time I didn't bring that darn cittern, could really use its magic about now. 

Peri:

Peri squeezes himself down between the corner and the corpse and tries to feed the rope under the great coils but can't quite reach. Arms're too short, but if I were any bigger I'd never've fit back here... He pushes his way back out, the putrid, slimy flesh giving way in places beneath his hands and feet. It is only with great concentration that he keeps his lunch down. "Aye, we'll pull it back just enough to open the door part way, then tie it off. On the way out we'll let it fall back in place to hold the door shut in case the eels try pushin' on it. Kei, think your little helper can crawl back there and pull the rope under? There's a spot it's humped up off the floor so he should fit through."

we'll pull it back just enough to open the door part way, then tie it off. On the way out we'll let it fall back in place to hold the door shut in case the eels try pushin' on it.

Peri finds this to be a workable solution. It's nasty, putrid work, but Peri is able to loop his line around the bulk of the sea serpent's body, and using his block and tackle, take the pressure off the door. (And with the slash of a knife, instantly return that weight in order to hold off an advancing force, if necessary.)

That just leaves the next issue of unbarring the door. (How to you plan to accomplish this?)

Gerrard:

Helping where he can, Gerrard mostly stays out of the way.  He doesn’t have any special skills for unlocking doors, so he remains quiet—even a bit pensive.

Boko during the hour if waiting (short rest?) doesn’t flinch when listening to the cries of the victim, her expression stony and silent… she does give a new series of searching, evaluating, weighing expressions to her companions, however.

She helps with the eel as best she can but she jumps into action when it comes to the door; she tries to fashion a certain kind of ice lever bar with dual arms that slide in the gap between door and frame, with the intent of lifting the bar she saw on the other side. 

Peeking through the gap and fashioning an icy tool from the water outside the cell, Boko tries to hook the bar and remove it from its brackets.

Dex Check to remove the bar: 7
Dex Check to keep the bar from falling and making a noise: 17

Boko fumbles with the ice tool for a long minute, but can't quite hook the bar outside the door. 
(Yes - you all may have a short rest while you were waiting for the torturers to leave.)

Boko sighs, underwater, which is an odd thing to see. She offers to go back under the door as an octopus and pull the bar up and set it down on the floor.

Kei 

Boko's icebar melts away too quickly to apply enough pressure to budge the bar. Pity. Thought she was on to something there. The plan sparks a thought in his mind though. He calls Krill to his side. He tries to indicate to the tiny crab how to tie a knot in Gerrard's rope. He then hands the end to the crustacean and points him to the gap above the door. Telepathically instructing it to run the rope around the bar and return back to him, he waits for Krill to return hoping his instructions made sense.

As Boko contemplates slipping through the crack again in Bokotpus form, Krill goes ahead and tries to slide through:

Dex check (to slide over door with rope): 4
Dex check (to quietly and efficiently tie up the bar) 12

Alas, while a flexible octopus can squeeze through the crack, Krill's hard, chunky shell is too thick to fit.

(Back to Bokotopus?) 

(Yes, Boko tries her wildshape plan 

Success. With octopus suction and careful leverage, Boktopus is able to remove the bar and lower it quietly to the floor. Then, one by one, the party slides past the winched corpse and into the dark torture chamber. 

This long room has five doors spaced evenly along the north wall, secured from this side with metal bars. To your left, by the east wall, rests an untidy pile of chains and manacles, leg irons, and bunches of keys. To your right, you see several instruments of torture — a wheel, a metal boot with catches and screws, a press, and a rack.

(Does Boko remain in octopus form?)

Gerrard:

Pulling a potion of healing from his belt pouch, Gerrard quietly hands it to Boktopus and requests, “Will you slide this under the door to the poor tortured soul?”

Qivys looks at Gerrard then goes directly to the cell where the prisoner is held. 
Qivys does his best to check if it is locked.
If unlocked he will open the door.
If locked he will hoist himself up to see the prisoner. Once he does he will use his "Telepathic ability to speak to the creature." 

 If locked Qivys will use Shocking Grasp on the lock. 
Damage: 3

((not sure how a "hit" on an inanimate object works.))

There appear to be five cell doors. The door furthest to the west is closed but not locked with its bronze bar (which is sitting nearby, against the wall.) The one in the middle is now unbarred and winched open against the giant dead rotting eel, thanks to Bokotopus and Peri. The one furthest to the east was unbarred earlier when Boko first scouted, but is barred now. The other two are also closed and locked with easily removable (from this side, anyway) bronze bars. All have small gaps above the door (some octopus-width, some not) but none that you're likely to see much through unless there's something of interest near the ceiling. To squeeze through, Boko or Krill may attempt a Dex check. (The one just east of the center cell has already been determined to be too narrow for either.) If Krill can get through, so can a potion (and so can Bokotpus.)

It's unclear where the torture victim might be, now. The last Boko could hear, he was in one of the cells to the east. (Did I suggest west earlier? My mistake!)

To open a door, let me know which one, and you may simply unbar it and open it.

(Gerrard and Qivys - which door(s) did you have in mind?)