Possible 2 Join friends not in party?

@fourzeez You can only join if your friend have a free slot in their crew. Just use the function to join your friends game on XBox Live.
But this is a bit tricky, you can only join if they started the session with enough player slots.
So for example: if 3 of your friends started playing on a galleon and said at the beginning they are a 3 man crew, you can not join to change it to a 4 man crew. If 3 of your friends started a 4 man crew and the fourth player slot is free, you should be able to join.