Orion says to the group, "We are about to enter the fortress, it seems.  What is the plan for finding and freeing our friends? Do you have any ideas, Prim?"

Orion says to the group, "It seems we are close to the fortress known as Kilkilfik, or Fort Kill.  Do we have a plan for rescuing our friends from this place?  We should talk about that before we go further."

"OK, if nobody can translate the maps, let's pack them away and they can translate them in Freeport.  First, does the underground map show the river exiting aboveground?   If sleepy is still alive we can ask him about the prisoners.  We want to find an exit so we can get the prisoners & leave.  Does anyone have Invisibility or stealth?  Will any of these hobs clothes fit us?  We might need to sneak in and scout."

Taxidea, as you go back down to the cavern to get Thor, you see Svelta waiting beside a small fire on the opposite shore of the underground river. She waves at you and Thor when she sees you.

Taxidea waves back to Svelta, gets Thor and heads back up to the stairs to rejoin the rest of the party.  

Oskar follows the party. "I'm not gonna be helpful if this is gonna be stealth. Chain makes a lot of noise. We should definitely try to make a detailed plan."

Orion responds to Prim:  (1) the map does not show any rivers, and (2) I can cast Pass without a Trace on the party.  My stealth is fairly good.

"Well ain't no way I'm going to pass for a hob."

Prim looks at the hob cadavers and Muses to herself.

"Hmm, would it make convincing disguises to peel their faces off & wear them as masks?"

(What skill would she roll to evaluate if that would work?  Deception, insight, medicine, performance, stealth or something else?)

"Prim, I'm 3 1/2' tall.  Even wearing a hob face - which again, I applaud your dark inclination, but also - no thanks - nobody will believe that I'm a hobgoblin."

"No, but maybe the rest of us could.  Maybe pretend you're a prisoner we're taking to the brig, if anyone asks."

Okay, Prim, roll a medicine check to see if you can successfully remove the face of a hobgoblin.

Medicine 22

And another to see if she remembers any diseases that could spread this way.  20

Using salt from her mess kit for a quick tan.

Orion looks worried.  "I've never been very good at lying.  I used to think that was a virtue, but it might be a drawback in this plan."  Also, what do I do with my bow and my short swords?  They're clearly not goblin-make.  To say nothing of my clothing.

"We can wear their clothes & weapons, maybe over ours.  And carry our weapons as booty or try to hide them under their clothes.  Anyone else want a mask?"

Orion reluctantly agrees to wear a hobgoblin mask,  his only chance at being undetected.

Okay. Prim is able to remove a hobgoblin's face, and she does know of some infections that may be caused by exposure to hobgoblin blood. Does Prim have any experience with tanning or making leather? The process for making a long-lasting mask would be similar and may take several days, unless you can come up with some combination of spells which could do the trick much faster. Otherwise, you will simply be wearing the hobgoblin's bloody skin and risking infection or infestation. (Hobgoblins sometimes have parasites like fleas or lice.) The salt is a good material component for a tanning spell, but you will need lime (calcium hydroxide) or chalk (calcium carbonate) as well as the hobgoblin's brain to make a properly tanned mask. Prim, roll a perception check.

Perception  8

Next to no chance of learning about tanning from a Noble background. 

But there's a chance it would be covered as a part of necromantic training.  Like "how to bind your spellbook in human skin" or something.

What does she need to roll to see if she learned anything about it? 

"Does anyone have a "Cure Disease" or "Purify food & Drink"?

Oskar can cast purify food & drink

Roll an Arcana check, Prim, to see if you learned about tanning techniques in your necromantic training.