So, right now we have Kai and Katherine, and Milena and Nessa interacting. I know Nym met Adrienne... Um.
Ooooh. Okay, so Bastien. What if he knew that Keiran's father, Aiden Hayes (a now-deceased NPC) was a potions master, and wanted to see if Aiden knew anything about curing lycanthropy? Obviously, his murder was not made public, so Bastien probably wouldn't know. After Keiran lost his memory, he has only recently gone through losing his father again, so that interaction could be reeeeeeaaally interesting. Especially since Keiran never asked his father about his projects much, and is now in Transfig instead of Potions.
On that same note, if he finds out that Avery is basically Keiran's sister (not by birth, but just from being around so much and not having a family of her own), he could bug her about it. Might be less awkward to ask a substitute professor than the Deputy Headmaster. But that's up to you. It would take his realizing she was close to them. But that could be arranged if necessary.
For Milena, I've also got Trisha and Katherine. Katherine is one of the more influential members of the DF, because her family has been part of the group forever, and her brothers were pretty involved. She actually isn't sure she wants to be part of it anymore, but if people turn to her, she would probably take the role on again since she needs some way to figure out who she is again after her medical issues.
Trisha, on the other hand, is a bit of a teacher's pet in that she is really against breaking rules. But then, she's almost like Hermione because she'll do it for the people she cares about, and then yell at them anyways after it's done. She's "neutral" but I think she floats in among the PA group. Or, she will once the werewolf laws are retracted. She isn't one, but her friends are, so she's been at Keiran's place with the other student werewolves who weren't allowed on the grounds. Once she comes back, I think she would be fairly annoyed with Milena if she decided to... I don't know, cause trouble or something. Trisha is also good friends with Nessa (ironically), so she wouldn't like it if Milena tried to get Nessa in trouble.