If someone is already in your Fireteam before you post a listing, the FF lobby UI should include them. Every time I create a listing for a 3rd player with my friend in my Fireteam, it confuses me that my friend isn't included in the lobby UI. You should be able to Ready Up while in Orbit without having to open the FF menu itself. I constantly deal with people confused on how to Ready Up because they're not aware that you have to actually open the FF menu itself in order to Ready Up. Summoning the Fireteam works very confusingly in that it basically acts as if you were kicked, and then moments later you're teleported into the Fireteam. I really can't stand that, tbh. I always forget that's how it works and I always think I was kicked when I join listings, and other people that join my listings have said the same.