This is what you have to do if you share same router with multiple NWN 2 players with own computers.
If two or more people are playing through the same router, then please change your client port in your "My Documents\Neverwinter Nights 2\nwn2player.ini" file.
Computer #1 set to: Client Port=5120
Computer #2 set to: Client Port=5121
Computer #3 set to: Client Port=5122