Fox will be arriving and leaving with Hope. He'll chat up anyone who comes around, but he'll try to avoid Frankie, just because he won't want a scene.
Mal is going to sit at his table and lurk. He'll talk to anyone who comes to sit with him, and give well wishes to the couple. He'll turn down offers to dance, and will probably get dragged onto the floor for Garret only.
Jason's going to hug Blue back and ask her for a dance, being his usual happy, sweet self. He'll dance with Cassie a bit, probably sneak her into a corner for a snog. Or three. >.>
Dee is going to be so happy, chatting up whoever she can, and trying to convince Dante for a dance. She'll dance with anyone and everyone who asks, and will be stealing Cassie at some point to get the dish on her relationship.
Declan wants to go, but is staying behind to keep an eye on things at the school, just in case.