So its all about thefinal quest and weighing the rewards? I can run both their missions ill just be asked to take sides in the final one? Say if do all but the last brotherhood mission, then switch to its opposing faction and do all their missions but the last. then can i go back to brotherhood and the faction i was in 5 mins ago?
Eh not really, moreso (and again, being vague on story here, not going to spoil anyone
when you pass a certain point the opposing faction is suddenly mentally aware you're with group A, so you can't do their quests. So you start the final missions by picking a side, the lockout point is actually a decent bit before that.