Hiya! *wave* I have a lot of babies, so here it goes...
Isabella might be a casual acquaintance. I can't see where they would be more than that being in different houses and different years. She would still be friendly because she pretty much tries to be a good person to everyone.
Zachary, I can't see why that wouldn't be a friendly acquaintance either. Zach is a good guy just a little shy. I am sure we could think of a way for them to run into each other despite the fact Zach is a 7th year Hufflepuff (he needs friends ^.^)
Camilla will hate him just on principle as she does all Slytherins. She feels like she has something to prove to them as a Muggleborn and that her stellar grades alone doesn't do it. So, there probably will be some bad blood there.
Piper... Hm. She's only a 5th year but I think we should have them meet. She needs a love interest or a friend or something. Lol. I have nothing to do with her character right now.
Kayley would definitely know him since they are both 6th years. They could be friends? Although, Kayley would definitely want to be more than friends. She loves to chase the boys. If they were friends she would probably try and talk him into going to the V-day dance with her *cough cough* ^.~