The school lets you run a router? At our school, the ip assigning is done with the schools switches/routers and if you try running a router in your room, we'll just turn you off. No sense complicating things. A wireless router is also a no go.
If you have 3 connections to the schools network, your roomates will not directly be affecting you. Aren't those 3 connections going to a switch/router somewhere of the schools. Its not like you have 1 port and you are using a switch to split it up.