I tried simplifying the problem statement, it appears to be counter productive. So here is the full story. I have a server (A) behind NAT, in a country that blocks a lot of websites and performs DPI.
You don't need a router. If you set the subnet mask on all of the PCs to be 255.255.0.0, then they should all be able to ping each other. Basically, opening up the subnet mask puts all of the PCs on ...