router firewall issues

I am a ham operator, and have two computers that are running the same voip communications software. The program requires that I do some port forwarding on the router, however when I try to set the router up for the second computer using the same ports it will not let me. I have tried to rename the computers but no luck. I need both of the computers to work on the same ports if there is a way to make it work. Best way to reach me is by email directly, put "router info" in subject line when answering plz. Thx for the help in advance.