Your best bet will be to try to ask your father to do his downloading at night, when the rest of the family is in bed.
Personally, if someone was doing this on my network, I would just take away their access in the router, but not allowing their MAC address to connect to the router. However, given the situation, this wouldn't be a wise decision for you, as your father would probably not allow you to use the network anymore. Unless you have a quality, enterprise type router that allows traffic shaping, you would have to do this through software on the laptop, again, not advisable....
So, in brief, your options are to reason with your father, get your own ISP account and set it up so that only YOU get access to it, or 3, continue with your guerilla warefare tactics, and possibly get burned in the future...