Sorry to argue here but it depends. if they are all playing in Lan or if they are trying to join an internet game.
For internet play with your 2+ computers.
If your not using port fowarding and your router seem to accept the convientional NAT transversal , then indeed you do not need to set different port.
BUT if you set port fowarding for all the machine, you MUST set them on different port with ImpulseReactorOptions.exe in the Demigod folder.
You cant foward all machine on the same port range 6112 to 6132
Machine 1 can be : 6112->6132
Machine 2 can be 6133->6153
Machine 3 can be 6154->6174
And so on.
Must be fowarded on the router.