FIRST TRY: I stayed in game, my husband logged out of destiny and joined my game through the main side menu from the dashboard. It actually let us join!!!!! Maybe it'll work for someone else too..... EDIT: Wouldn't work the next night but after many attempts I think we've found the trick. Both players go to tower, team leader stays in tower. 2nd player quits game while in tower, and then joins on leader from their profile. It has worked twice so far tonight and seems to only work this way.