this has been answered by frunple. do a search for "multiple remote desktop".
A note on security:
- avoid using port 3389 on the router
There are hacker programs that scan the internet for RDP 3389 listening computers then try to hack into those computers. If they can't hack into 3389, they can also look for other listening ports on the same router and try to hack those computers. Use a port that is very different, maybe something in the 50,000s.