How do I go about adding a member to my group? Is it simply adding them to my friends list in my group?
There isn't really an official "membership" in a group right now.
You can add them as GMs to specific event and when you assign their GM badges, you can issue them as needed with or without them being your friend (since badges come from the company profile, nor your personal one).
The key for either is having the email address that use in their account in the Gen Con system. As long as that is accurate, you should be good - just list them on the events and issue them their badges when that is ready.
Director of Events
Gen Con LLC