Eh, I don't often answer "what do we players do" threads on ENWorld. Plus, it's hard to answer without giving free prophetic hints, eh? If you want prophecy, have the cleric cast
divination. "Ready oil and open flame light the way."
My generic advice -- first decide what you want to
do with your spells. Sneak around, kill things, find out info, all of the above, whatever.
Then consider what you've encountered: shadows (that appear to replenish themselves), fiendish fish, a fiendish octopus, a fiendish chuul, fiendish stirges, skeletons, zombies, wights, a fiendish dire boar, a fiendish shark, fiendish centipedes, fiendish spiders, traps, one or more presumed bone devils*, and something that whispers in ears at a distance.
(*Though it could've been a couple of low-level sorcerers with
invisibility, fly, and
wands of wall of ice . . . )
Certain patterns emerge; one might conclude that SR, fire, & cold resistance will be relatively common. As almost always, sonic resistance is sadly lacking. Fiends from Hell (assuming they are all from Hell) have a distressing lack of electrical resistance, too. THere are a few juicy targets in that list for mind-affecting spells, but all the vermin & undead are immune to such spells.
Other than that, I wouldn't try to come up with a detailed plan -- you don't really know exactly what kind of mastermind is guarding Bloody Jack's gold, after all. Pick a strategy, be flexible, and conserve your ammo (err, spells) -- don't bother blasting dinky undead that the cleric can destroy with a casual wave of the ol' Rune of Pursuit. Unless said dinky undead are holding the cleric's head underwater, of course.
You might either convince the druid to be a bit more flexible with his wildshaping, or rearrange the line of march so the dire lion is closer to the front (and then hope he doesn't end up being the dire trap triggerer, or regretting the sad armor class of your basic dire animal).
Decide how you're going to get in and out -- teleport magic, fight (and swim) your way in & out, look for a secret passage (and hope whoever built the place put one in, for some mad reason)? Camping out inside is a Bad Idea; either skip it, or come up with a good way to make it not a bad idea; it looks like walling yourself off is viewed as an invitation to sustained siege.
Rope tricks are neat, but potentially dangerous. They
can be detected, after all, and if you think being ambushed while sleeping is bad, try being ambushed while sleeping while being dumped from 30 feet in the air...