"Is the problem that you don't believe me, that you do believe me but don't want to interact with whatever is going on, or that you know what's going on and are okay with it but don't want to explain?" 

"I don't see any particular reason to take your word for it, but even if I did it's not my business to second guess her."

Brenda is aware that some people are such lousy bosses that their employees would rather let them be eaten by a demon than risk getting yelled at. She is also aware that there are demons who wear their victims' faces. 

She doesn't know, but can imagine, that there might be things that can cause false positives--or false negatives--for her Aeon sight. Fortunately she has a way to double check. Detect Magic. Detect Fiendish Presence.

There's a faint fiendish and magical aura around both of them; not enough for them to be demonic clerics or demons that could hide from her sight, but like the kind you might get from a spell or weak magical item or similar.

Brenda turns like she's given up and gestures to Wenduag and Seelah and Nenio to follow her into the nearest alley.

"There's some kind of demonic effect on them both; I'm worried the demon in the building has them enchanted. I have a sorcerer spell that might be the one that helps people throw off enchantments, but I haven't actually cast it before and it could be a different abjuration that won't help. Seelah, Nenio, do either of you have something more certain or is 'try my spell and see if they snap out of it' our best bet?"

"I could pray to Iomedae for a solution; she sometimes gives paladins the ability to use magic like protection from evil, and helping an innocent person escape a demon might warrant my getting it. But I don't know if this is more likely to work than your magic and praying for spells is supposed to take a while."

"If you have a new spell, you should definitely test what it does! Abjuration is one of the most boring kinds of magic, so I don't have protection from evil prepared, but if it doesn't work and we need to I suppose I could cast it with my bonded item. Or if you think they're enchanted we could just knock them out."

"I'm thinking try the spell and if it doesn't do anything either knock them out or sneak in the back and deal with the demon directly."

"If we go in through the back, I don't have enough spells to turn everyone invisible, but I can just put up an illusion to hide us."

"I should try to copy the invisibility off that one kind of demon, but first things first."

She walks up to the guards again, smiling politely, then pokes them and casts what is, in fact, the sorcerer form of Protection From Evil.

The spell fails to accomplish anything other than make it obvious she's using magic, and the guards are not happy about it.

"Hey, what are you trying to pull here? Trying to enchant the city guard is a serious crime, miss, don't think that being an adventurer will let you get off free. I advise you surrender, or you won't like what comes next."

They raise their swords at Brenda.

Valid as far as it goes but if she'd warned them they might have been required to avoid it. She knocks their heads together with carefully calibrated force, silently grateful that they'll be fine later because nobody ever gets concussions in Dungeons and Dragons.

A pathfinder character with class levels is unlikely to be permanently or seriously injured by nonlethal damage, since they have more than enough real HP to sap up any accidental overkill that leads to ordinary injury. This does, however, mean that they are significantly harder to knock out, and while Brenda slamming their helmets together rings them like a bell it's insufficient to put them down. They'll try to stab and slash her, respectively, since those are the least awkward angles from their positions.

Their swords clang off her variously magic-item-boosted armor and she bonks them again. She will apologize later.

That'll drop them! Once past the door, there doesn't seem to be any more guards; the demonic presence is across the ground floor in what seems to be a room for entertaining guests.

Wenduag is better than the rest of them at sneaking; does she want to try to scout ahead or should they just barge in all together? (The Message cantrip is very handy for this sort of thing.)

With the help of some invisibility from Nenio, Wenduag will do just that, making sure to walk quietly and minimize her exposed profile in case whatever demon is in there can see through invisibility. About a minute later, she reports back in a whisper.

"The person in charge seems to be a female demon; looks like a succubi, but maybe there are other kinds that look similar or it's something else pretending to be one. They don't seem ready for a fight; they're sitting in a chair with their feet resting on someone, I couldn't see who, while two guys attend to them. If there were any other demons or combatants there, they were hiding, disguised, or invisible, but I don't think there are and I'm pretty sure she didn't notice me."

"Great, thanks. Let's all go at the probably-succubus first; if there are any other demons I should be able to tell when I have line of sight. If we kill her or knock her out will everyone she's controlling immediately recover?"

"Even killing her won't do that. If she's using suggestions, that'll wear off in half a day or so, but any charm or dominate effects could last over a week if they aren't removed."

"Figures. I have two more spell slots, but given how well that worked last time we may not be able to do better than knocking them all out and dragging them to someone with more options."

"The church will definitely be able to help them, but succubi are dangerous for a reason. Maybe if you can make her surrender like Minagho she can undo it, but that sounds risky if she gives them a harmful order instead or uses the opportunity to escape; getting them help might be safer for them."

Brenda nods. Anything else before they go in?

Nobody else has anything to say. The four of them can sneak up to the room undetected, though Seelah has to be very careful about her armor not making too loud of a noise, and avoid anyone detecting them long enough to make it to the doorway. Inside the situation is largely as Wenduag summarized, though apparently in between then and now one of the men attending to the demon was told to bring her some food.

Brenda waits until she's maximally distracted by taking a bite and then charges in, swords blazing. (Metaphorically. No shadow demons to dazzle this time.) She's expecting the controlled humans to potentially be used as human shields, so she needs to get between them and the succubus as quickly as possible.

The succubus' first reaction to an enemy in full plate armor charging her is to try use her magic, but a pair of arrows from Wenduag interrupt her before it becomes clear what she was trying to cast and she fumbles her concentration, allowing Brenda to reach her unimpeded.