Have been add you just get to joining one quickly. These will be your partners and friends. You can have dorm wars in the Arc area, just cause your in one Dorm doesn't mean you can't be friend with or date people out side your dorm. Any question about dorms add here.
P.s. If you we're wandering yes you can change from one group to another. Because this is a school you have the abality to transfer from your dorm to another dorm.