It has been my experience that you can only get 2 players from the same household(or any similar situation) to play Starfleet when either of these conditions are met. How you meet them though is up to you guys, not me.
1-you have same CD game installed, but are not using the same system(ie: Dynaverse, or GSA in same room). This would allow father and son to play, but one in Dyna, 1 in GSA, or 2 in GSA, but not in same room.
2-you have 2 differing CD games installed(using seperate CD-Keys). This works for GSA, but not Dyna.
3-same CD intall, but 2 seperate IPs. Works for Dyna, and GSA.
4-2 different CD-Keys(or games), and 2 IPs. Works for Dyna and GSA.
I hope this helps.