What are you remotely connecting to? You won't be able to see the computer by name, only by IP address.
Port fowarding will be required. You'll want one port to send to computer a, another port to send to computer b, and a third port to send to computer c.
By default most remote admin programs use port 3389. So you could set up port 3389 for compa, 3340 for compb, 3341 for compc.
When you go to RDP you would select your IP address that currently connect you to compA but specify port 3340/41 for the other computers.