Hey Chele, it's Jenn! The 30s are the best years to be alive, don't let anyone tell you otherwise!
I have Marcus Flint and Delilah Moon* (dlilah) (formerly Williams), both coming in with their Quidditch Village histories (and current lack of memories of those events).
Marcus & Katie: He mostly remembers her as being part of the crowd of Gryffindors that he despised. He finds the fact that people are showing up from different time periods in their lives to be weird (not that she can do anything about that). He probably doesn't go out of his way to talk to her, expects the worst if they do have to interact, and will be very surprised and suspicious of any niceness she extends in his direction. That being said, it could certainly be interesting to throw them together in a new environment, so let me know if you want to try something, maybe something on the calendar could be interesting?
Delilah & Katie: I know they are not exactly from the same realities, but assuming that Spinnet family parties were a thing in both worlds, they could have become friends through Katie-Alicia, and Delilah's connection to Emilia and Leo? In any case, Delilah's going to try to befriend all your characters at some point, because that's just who she is.