Giselle, if you are straight up with them and tell them that you will only be there for a short time because of your mom, I don't think there should be a problem. You may not be able to live in the house but you should be able to participate otherwise. And once you are at the 3rd school they probably won't care if you decide to stay here. Just think, you will end up with three times the sisterhood!
ps - Good girl for moving to be by your mom. You'll always be very glad you did.