Greetings,
Asked a thousand times and Frontier says no.
A player can have three crew members but they cannot be activated without a fighter bay. Then only one can be activated at a time. They can pilot a fighter remotely or the ship. That's it. No manning turreted weapons, driving an SRV or seeing them in the cockpit. Combine a crew member with a live player in multi-crew (that is visible in the cockpit) there are advantages. My impression is that Frontier might have had a useful purpose for three crew members but never implemented it. Maybe it was a combat balance test where adding a feature would make one player have too much of an advantage over another not using crew members. What is your guess?
The only use was at one time crew members could die permanently thus having two more as a backup. This upset many players getting their pilots to Elite ranking and Frontier listened. The game was updated so when dying a crew member can be saved on the rebuy screen. Then having more than one financially and for combat ranking is very inefficient.
If they could be activated without a fighter bay they have no useful game purpose except if the player is in an SRV and the crew member is flying the ship overhead with air support. Could be fun! We would like to see them in the cockpit but again Frontier said no. Maybe live players have more polygons than crew members or seeing both crew members and live players in the cockpit is a programming problem causing a crash to the desktop. Then along comes Odyssey...
A Scorpion SRV can carry two live players in multi-crew but not a crew member. Again a player on foot and a crew member in the SRV with ground support. Maybe another in the ship with air support? Awesome even if they are not very good except for specific moments! Oh wait there is that combat balance test Frontier is always worried about. Well we can imagine...
Regards