Maybe you might make some new friends? I'm in the more the merrier camp but I don't expect everyone would feel that way.
Although, on reflection the celebration is being held at your parent's home and not yours. I probably would feel a bit weird sayng to my parents that my BIL's friends were coming over, especially if they were going to be eating and drinking. I don't think they would mind but yes, a llittle odd unless as PPs say they are Christmas 'orphans.' We always have a few randoms every Christmas because that's just how we roll.