Get equipment that can do what you want and set up your layer2 network in such as way as to prevent hosts from being able to see each other over it. It has nothing to do with the router since people on the same subnet/layer2 infrastructure do not need to go through the router to "talk" to each other.

thank alot (Feklar) for answering ..

but i have never used layer2

could you please explain how to do that ?

Layer2 refers back to the OSI model for networking.
http://en.wikipedia.org/wiki/OSI_model

Layer2 is would be devices like switches and access points. Layer3 are things like routers. Two devices on the same subnet/layer2 network can "talk" to each other directly without using a router. What this means practically for you is you need to invest in switches and access points that will actively prevent hosts from seeing each other on the same layer2 network. Client isolation on access points, VLANs or port isolation on switches.