Vlar would be in the rear, letting others take the brunt of any traps or ambushes they might come across.

I need some stealth checks if we are sneaking in.

Kuatho stealth to sneak in :  19  

(Splint causes disadvantage on Stealth checks.

If Kuatho is going ahead, and waving when it is time for the party to move up, then Jecob will stand still.
If the party is staying together, then Jecob's Stealth check is in the "spoiler".)

Mist is hanging toward the back of the group, too. I'd say second to last, in front of Varlan.

Stealth: 20

Kraven Stealth: 19

(( lol...hoping this is a group check! ))

Varlan offers a brief prayer to the Great Maker as he moves forward.

Stealth: 21

Vlar stealth is a 9... good thing he is in the back.

The chamber contains a well-lit library. Tables and bookcases surround the room, filled with tomes, lit by smokeless torches hanging from sconces on the wall. An ornate purple rug lies in the center of the floor, depicting a robed cyclops leaning from the prow of his ship, feeding a baby dragon to a massive kraken. 

At one of the many tables, an Imp organizes books, some of which that are larger than her.  As you enter she does not notic at first but then hears Vlar and turns invisable.

You hear Kalvikodas' voice saying "Get out of my libary!"

Kraven hops into the room as he reaches into his backpack and pulls out a torch and lights it. "Getting tired of your games fool, show yourself now." As he holds out the torch dangerously close to a bookcase.

You hear now a feminine, demonic voice say "Go a head I don't care."  Then a book flys out of the same area that the voice was coming from.  22, as the book flys you see a figure, one that looks similar to Mist's friend Tuk, she has brownish red skin and is wearing sea weed as clothing.  Her eyes glow red.

The book flyes over Kraven's head.  I also want to make sure we understand that the figure came into vission after throwing the book, but then went back to being invisable right away.

 A quiet, gravely chuckle can be heard from another corner of the room. Mist shoots a dirty look in that direction.

"That doesn't help," he grumbles.

"Who's tryin' to help?" comes the retort. Mist closes his eyes to compose himself momentarily.

The overstuffed halfling holds a hand up to Kraven and looks back to where the imp was last seen.

"Look. We're jus' tryin' ta get out o' here. Your Kelvin o'er yon 'as been makin' it reeeeal difficult like. What say none o' us sets fire t' the place seein' as how we don't know a way out just yet? We jus' want ta have a sit down with your boss. Can yeh help with that at least?"

Quote from coachmanak >>

... but then went back to being invisible right away.

Jecob moves forward to stay within 5' of the invisible imp, since he has blindsight with a 10' range.
Once he has located the imp, he will point with his off-hand, so the rest of the party is also aware of the location.
Not attacking, but hopefully this will show the imp that cooperation would be better than playing these futile invisible games.

("Blind Fighting" is one of the fighting style options. Figured it would be useful when deep diving and the water is murky.)

It takes Jacob a moment but he finially corners the Imp, she then yells out "FINE! WHAT DO YOU WANT?!"

Kuatho looks up innocently at the voice and says “We want to be out of here, wherever here is.  So that we can continue our journey.  Exploring the world.  Not trapped inside of this place.”

Mist shrugs and looks around at the group.

"Didn't I just say that? I mean... His answer sounds nicer than killin' ol' Calvin, but honestly I'd be ok with either one."

The imp drops her invisibility.  

"I would like to help, but I can not.  You see Kalvikodas keeps all the souls he's captured in magic crystals that make up his Library of Souls. Destroying one of these crystals is very difficult, but I have seen it done, magic seems to work the best.  My soul is not being held in his libary right now, which gives me the ability sometimes to leave the libary, but not for very long."

Glerm stomps his foot, "Long enough to take things from me!" and he shakes his hammer.  As he is shaking about you see something, that you would have seen but never thought about it before.  On one of Glerm's ribs hangs a chain with a crystal on it.

"OHHHHH shut up you, there, there is my crystal, give it over, and someone break it so I am free!"

What do you all do?

Varlan looks between the crystal and the imp. He gingerly reaches inside the body to take hold of the crystal. He holds the crystal in his left hand as electricity begins to flow over his right hand, though none reaches the crystal.

"What a fascinating device. Such a small thing to contain a soul." He stares into its depths for a time before turning to the Imp. "And you say that there is a crystal for each of his slaves. Does Kalvikodas himself have a crystal here? If we break this, will you aid us, or just flee?" he asks.

"Yes, each of his slaves, he does not have one, not that I have seen at least.  And I would only make sence for me to aid you their in no other way I could leave."

Glerm speaks up, "If she is going with I will not.  Free her by all means but after that she can stay here and perform her gags on others, until she can free herself."

"OHHHHH Glerm your such a grumpy such.  Its just a little bit of fun."  She dances her fingers along books one step per syllable while she is talking.