I will go ahead and comment here for both (all "three?") of your girls here!
I don't have any Bravos, but I do have a Foxtrot who'd room on the same level as Cortana. That's Reaper here, who also runs the morgue and controls the dead. Generally creeps out everyone, but she tries her best not to, really! She comes across as a generally nice, friendly person, though it's mostly facade. She likes to fantasize about dissecting some of her teammates to see how they tick, but that's not something she shares with the class. :)
Leah steelyeyed is the most important of mine for Helix, since she's her handler. I would looove for her to be the one who can trigger the switch between personas, and Leah would also love that lol. As a handler, she constantly pushes her supers' boundaries and pushes them to be better than they are. She'll make sure Helix has plenty to have to heal, even if Leah has to cause the damage herself. Onslaught heals himself, so that'll probably fall on Backlash. She won't have too much interaction with Cortana.
Blitz smoothasglass is my other Alpha, a damager and Backlash's brother/roommate. He could totally have been a brief past fling who dropped her when he realized the crazy. Nowadays he's only down to one fwb anyway, Pixie. He's a pretty friendly, outgoing guy who'd get along well with Helix (or at least, half of her?) and Cortana both, and wouldn't mind playing some video games with Cortana during his Nirvana time.
Medic needamedic is my Echo healer. Big old grouch, Grumpy Cat in the flesh, has been in the program for something like 26 years now and was turned in by his parents as a kid. He'll grump at both girls indiscriminately because that's just how he is, though he'll probably be less irritable with Beth than with Liz, and Cortana would be somewhere in the middle because dance parties make him :|. Just like everything, though, really. XD
Livewire superconductive is my Juliet damage and unstable herself. I think she and Helix could either get along very well or hate each other, or alternate between the two with mind boggling frequency (which is more fun~). She's a bit like Liz but maybe with more violent tendencies and a criminal record she'd love to expand. She'd probably hit on both Helix and Cortana, would happily join in on Wet Floor dance parties and probably try to turn it into something less appropriate, and would jump between friendly and moody in a heartbeat.
I've got a sixth I'll probably be holding in the next few days who'd get along especially well with Cortana, but I have to wait on her. :D