[masraum]

It'll depend upon the capabilities of the router that you get.

If I understand you correctly, you'll need something capable of creating 3 networks and having those 3 networks firewalled off from each other, but able to access the Internet. At the very least, you'd want the ability to create an "access list" between the networks.

To confirm, what you want is something like this where you've got a network for person A, another for person B, and a third for guests. And you don't want anyone on any of the three networks to be able to access the other 2 networks. Is that correct?