Brenda can't do that either, but she can go investigate some corpses. Who, how many, dead of what?

Dead of what is easy to figure out - it's ghoul fever, judging by the fact that the smell is coming from ghouls. Who and how many is much harder to figure out, but if she heads out of the chapel itself looking for ghouls she can spot five of them pretty quickly - at, admittedly, about the same time they spot her.

Brenda applies the standard first-line treatment for end-stage ghoul fever (slicing them in half).

Likewise. 

The ghouls object to this, and the arrows that start sprouting from their flesh get a similarly poor reception. In the case of the ones closest to Brenda and Seelah, this doesn't much matter, but one of them manages to get to cover and another lunges for Ember as the presumptive weakest of the group.

Seelah goes after the one going for Ember. The girl is a lot more dangerous than she looks, but you still gotta keep the casters out of melee.

Brenda chases after the other one in case it means to come back with friends.

Ember ducks around the blow, but it's not alive enough to go to sleep and there's nothing else she can do to a ghoul without killing it. She's considering whether killing a ghoul is enough more like saving someone from being hurt than it is like killing someone that she should be healing it, but Seelah cuts it down with a sword before she finishes.

It mostly just meant to get a stone wall between it and the sudden adventurer party to try safely shooting arrows but if she's just going to vault over the wall like that it's going to try legging it instead.

Brenda is aware that ghouls have to eat people to live and also that being a ghoul is worse than the majority of afterlives, so when she catches up to this one it gets skewered without much in the way of emotions.

Personally he rather preferred staying alive, but apparently nobody was asking for his opinion here!

...Apparently that was only the last of the ghouls in this group, because from the sound of things there are a whole bunch more of them on this mountaintop. Some of them heard the commotion and are headed over to investigates.

The actual goal here is to find any further prisoners and any important intel and then get out, but if they need to kill another wave of ghouls first then okay.

Another wave might be a slight understatement; this mountain seems to have rather a lot of ghouls, and a fair few of them are significantly more dangerous than the ordinary kind. If whoever is in charge here doesn't know about her arrival yet, they probably will soon from all of the commotion, and in the mean time a few of her companions are rather squisher than she is.

There aren't any rescuable prisoners up here and she doesn't want to just keep doing this until someone in the party gets hurt. Fighting retreat back down into the building to check out the floors she hasn't seen yet, keeping everyone close enough together to Teleport out if things get any dicier?

The next level down below her initial entrypoint does not appear currently in use; though it's certainly set up to hold more prisoners and probably did at some point in the not-too-distant past. 

The stairs leading down to sublevel three, on the other hand, are covered in a thick layer of dust. None of her companions so much as give it a glance while they sweep the rest of the floor.

"I know it looks like nobody's been here in ages but we should check it anyway--wait, can you guys not see these stairs? We should definitely check them then." Emphatic pointing with both lower arms.

They can't see it, even with her pointing it out; Wenduag tries to walk in the direction of Brenda's arm and ends up curving without noticing it. 

It's not clear whether the magic that turns them aside is a bit less powerful than the illusion or if it's just that elves are a bit more resistant to compulsions, but Ember can walk into the solid wall; even once her hand sinks into the seemingly solid stonework, though, her eyes still insist that it's a genuine barrier.

"That's really weird!"

Seelah sticks a hand through the wall next to Ember's. "Yup. It has to be an illusion but I still can't stop seeing it." She tries leaning forward a bit and sticking her head in.

Her head can go through just fine as well. It's a rather discomfiting experience to experience the sensation of your head being engulfed in solid stone, but she can still breath just fine and it doesn't seem actively dangerous.

"This is very strange. I can't see anything without going in farther."

"They probably didn't illusion everything on the far side unless it's a really small area. Let's all hold hands and go down slowly. Uh, Wenduag, just hold onto me and Seelah and go where we're going."

They'll go along with this!

As expected, a few feet past the stairway the illusion fades and everyone else can see the same dusty steps Brenda can. The path takes them a good fifteen feet further down into the earth before leveling out into another hallway, still in a similar state of disuse. Each side of the corridor bears a pair of large double doors, securely shut, but the door at the other end is open. Ordinary eyes would have issues picking up details in the gloom, but to Brenda it seems to be a library.

Jackpot.

She has just enough self-control to check the books for trappedness with Detect Magic before she starts shoveling them into the bag of holding.

Wizards (affectionate). Seelah keeps both eyes and a Detect Evil out for ambushes.