Family only ceremony

Due to the amount of people invited to the wedding my Fiance and I have decided to do a family only ceremony and invite everyone else to the reception(since a lot of people just want to come for the party). The small issue we are having is that he considers a lot of his close friends as family and vice versa. How do you make a cut off for this and who should be priority within his family friends? I don't want to put him in this position but at the same time we need to make a cut off.