Alright so I have computer A,B,C

Computer a resides on its own network. Computer B,C are on their own network together.

So computer A is a server that recv's multiple socket connections at the same time from clients B,C over the internet. The issue for me is when they connect via TCP to the server each one socket the server handles each connection perfectly fine but when they both add a socket connection making 4 connections how can I make the server tell which sockets belong together in a group by Computer B, And Computer C, so I do not get them mixed up?! I do not want to send information to computer C that needs to go to B when feeding streaming information. Should I on connect send them a Large random number that they send through with every socket connection so I know that the new connection is coming from a existing computer that already connected? Ideally I would look for the IP being different but both of them coming from the same WAN address will not help in this case =(