Definately see what your college says about tanks/pets. Mine is pretty good about fish...you can have up to 20 gallons of tank per person. Also find out what kind of room you are in...the beginning of freshman year, I got stuck in a triple in a double size room...no room for anything over a gallon.
What are your bettas in now? You could set up a pair of 2.5 gallons with dividers, and that would take care of 4. Are you planning to bring your other fish, too?
When I came up to college, I wanted to bring a 2.5 gallon and my betta. We waited on the 2.5 gallon for the first trip, to make sure there would be enough room for it. Then I brought it up after I went home for a weekend. You shouldn't have a problem with a betta or 2, but your other tank might cause a problem.
How are your parents about taking care of fish? I know my Mom is great, and she loves the little angels and kuhli loaches that I left her...