Frustrated with Port Forwarding

I need to be able to logon to remote desktop into 3 PC’s on my network and the server. I have only got port 3389 and 3390 to work. Can anyone provide any suggestions to making the others work.

I have a Dlink wired router that has up to 8 ports available for port forwarding. I have tried 3388,3391, and multiple other ports to make this work. Currently 3389 and 3390 are setup to forward to workstations and are working fine.

I really need to be able to get into the other PCs and server using remote desktop. Remote desktop is setup and enabled on all worstations.