Alicornutopia

Note to self: In the future, consider coming up with a plot before starting writing a story. ;P

Denice Camus/Rescue: A Dusk. As such, autistic and near-nonverbal, which goes rather worse for her on an Earth than on Carp. Triggered at like 8 years old when locked in an isolation room with the lights off for an extended period of time; figured out she was a parahuman at like 11-12, escaped from the institution she'd been living at (Ponderosa Center) at ~13, is ~15 when the story starts. (Note that Lurker thinks of 12-year-olds as adults.) Homeless, relatively minor PTSD, extremely worried about being reinstitutionalized, particularly if it's known that she's a parahuman. Moves regularly (sticks mostly to the east coast), generally breaks into at least one institution in every place she stays and messes with their stuff (breaks locks on isolation rooms, destroys/steals restraint equipment, etc), occasionally also rescues people from institutions, depending on her ability to support those people while they learn to survive on the streets.
Rescue's powers: Extreme hearing, even more extreme auditory processing; detailed realtime echolocation-based map, details vary with range and composition of intervening material but she can detect small details at ~1 mile range through dirt, a usable overview of the area at ~5 miles range, and Behemoth/Leviathan at significantly longer range through dirt/stone or water; sound/echolocation based awareness of nearby things; enhanced ability to recognize sounds - can e.g. recreate the code used in a keypad lock where all the keys make 'the same sound', given an opportunity to press the keys and see what sounds they make; enhanced ability to recognize accented speech, words in foreign languages with unusual sounds, etc (no enhanced language ability, though).

Sebastian & Carl Banks/??: A Swiftness & his brother; cauldron capes. They 'volunteer' at an institution targeted by Rescue; Sebastian notices her while she's planning a raid, they assume she's targeting them and go after her.
Sebastian's powers: working memory disruption (makes you think you just did the thing you were about to do, though it's possible to notice you didn't actually do it if you check your surroundings) and synesthetic attention awareness (things that people are paying attention to 'light up' in relatively distinctive colors, even if the person paying attention is out of sight range)
Carl's power: Drains energy (causing tiredness/sedation) to charge an internal 'battery', which can be tapped to provide temporary regeneration. Sells this healing to various parties, including full-on villainous capes, could arguably count as a rogue if he wasn't nonconsentually draining people to power it.

About the keypad lock: are you sure that interkey variance is greater than intrakey variance? It might be literally impossible even with perfect hearing and auditory processing to do what you describe without hearing the password multiple times.

That's the kind of impossible that parahuman powers can help with, though, like Tattletale's impossible deductions.

Yeah, but it sounded like these particular powers should not be able to do that particular thing. The only extra information comes from sound. Unless she is actually good enough at sound localization that she can hear which key is pressed that way and does not need to listen again, or unless I’m wrong about intrakey variance being larger.

I'm pretty sure inter-key variance is higher than intra-key. Inter-person might be higher than either, but she can compensate for that, particularly with N>1 datasets which she's usually able to get. (This is the kind of thing she can do from a mile away under usual conditions.)

So, the main thing I still need here is general motivation, for S&C - of all the things they could be doing with their powers, why this one? (Also cape names but that could actually not come up, depending on how I write it.) Straight up money/lifestyle is part of it but I feel like if that's their only motivation they come off as pretty strongly rogueish rather than villainish, and I do actually want them to look like villains.

I do know based on personality that Sebastian is much more into the 'being a parahuman for fun and profit' thing; Carl would be straightforwardly heroing if it wasn't for him - or wouldn't have powers at all, as Sebastian is the one who introduced him to Cauldron and paid for his powers. I'm also not sure what Sebastian was doing before getting his powers and between getting his powers and getting Carl his; Sebastian's powerset probably lends itself to cheating at some kinds of games of chance so he might've been doing that (does anybody know enough about how poker works to know if it'd be useful there?), but that seems kind of overdone to me, I'll have to think about it.

I like making up cape names. Lapse and Ebb?

Lapse is pretty good. Ebb not so much, he prefers not to think about that side of his power more than he has to.

Asclepius?

Ooh, quite possible.

Edit: More likely Cadecus, though. "It is often mistakenly used as a symbol of medicine instead of the Rod of Asclepius, especially in the United States", says wikipedia, and '...yeah, it me' says the character.