hi,
there is not such software that can control other pc's network traffic. (i guess so) because we will need a server to do that.
u will require a server to limit and control amount of packet transfered to a computer.
so in your case, u r in the disadvantage side when ur house mates are using more bandwith in downloads.

sometimes routers will 'hang' too when it had to deal with too many packets (too many people downloading) so may be u should restart your router once a while.
and why don't you exploit your routers features, there might be some functions to restrict access to certain website for certain time period. But it will be surely not fair to your house mates la. haha.