If you’re going to do that, get at least two people, but I recommend three more.
This is because when you add a member to the group, HP for the monster increases. But it doesn’t scale by number of people. One added member leads to a monster with the HP of an assumed 4-person team. So in essence you can make things harder on yourself by adding just one other person. Not always a problem but Nerg is tough as is and adding HP to him isn’t worth one extra person drawing aggro.
This is never explained in the game.