If you were in your home, you could keep pre-purchased content in iTunes on a computer and then multiple Apple TV's could access that content over a local network. No problem, it works well.
However, the license you have agreed to when purchasing this content does not allow public broadcast, whether or not you are charging for this content or not.
I am not at all sure whether additional entertainment licenses that might be available in your location might provide a solution, you would have to look into this yourself.
If you want to block others from using their own Apple TV's, you should be able to set up a firewall rule to block access at your wifi router. The ports used are listed in the following Apple KB article. Depending on your hardware, you could either just block ports, or if you have a firewall of your own inbetween the router and your clients, you could right rules based blocking. Simplest thing is just disable port 5353in your wifi router(s)), but you could also use a rule based firewall entry to block the application, regardless of port.