Hey Mikaela I'm sorry it was such a terrible day. Maybe I missed something here but did your dad consider having Mixed Up and the kittens fixed and vaccinated and let them live in the back yard? It sounds like Mixed Up may have been a pet at one time and got lost or was discarded. It sounds like you're very good with animals.
I think you should give the friends thing more time. The first week of school is frantic and sometimes chaotic. It isn't easy to assess a situation under those conditions. Being the new kid is very difficult.