There are parental controls on the xbox for a reason, one of your family members really needs to set a limit as to how much time it can be played in a day (which is one of the controls that exist), especially after the TF2 incidents.
Gaming addictions have become more common over recent years so you might get better advice from a specialist centre/website to do with gaming addictions. It will probably help you, your family and your brother better in the long term. I don't know how old you are, but acting as an authoritarian sibling isn't going to go down well with your parents, even if it is necessary.
Also, is your brother anything like the embarassing kid in this video? Maybe your can shock/scare him into doing something by showing it him?
http://www.youtube.com/watch?v=Lgw2slDfx9Q
