It's definitely not you or your connection. It's Destiny.
It's ridiculous that it's been over a month since Rise of Iron's launch (which caused the issue in the first place) and we've gotten nothing but a 'Yep. It's a problem we're aware of.'
Being completely unable to play with friends in the same house save for seemingly random flukes where the stars align and it lets people join each other is insane.
English
-
So this is a work around that seems to work 100% of the time. Trust me when I say I have tried EVERYTHING else! 1. Both players load the game and go to the tower. 2. Both player at the same time press the XBOX button and quit the game. 3. Both players at the same time start destiny again and this should generate a 'WEASEL' error. This should usually happen to both players. 4. Close the error and continue to selecting your characters. 5. You should now be able to join the same fireteam team. I know it's a ball ache it this does genuinely work. You can even leave the fireteam after and you will have no issues rejoining. This is a fix for as long as you are online but the next time you play you will have to do this again. Just goes to show that this is truly a bungie issue as to get this to work no changes to any network settings need to happen. Hope this helps.