Even with 4 people it isn't too hard, just got to be smart about it. When 1 person can't do a proper nade jump, just tell that person to hide until he gets warped at the next checkpoint, use one person as a decoy as one assassinates the elite/brute in question. when one person dies you just check point instead of you dieing and having to restart or save/quit it over and over again. I did it with me and a friend it took us a hour ( that damn FM didn't want to die lol). When ever you do a laso I suggest you use the guide I linked above