Most routers have ways of blocking mac addresses. (Or at least the all that I've worked with) I'm assuming that you know how to access your routers page or whatever it's called.. (192.168.x.x). Look under wireless, or security, or settings, or features, anything along those lines.
Look for something called "Mac Address Filtering" or "Mac Filtering" and then go there and put in all your pcs mac addresses that go through that router, and then update your router and you should be set.