We stayed in Yellowstone last summer and never really counted how many people were at each site. We were gone most of the day exploring the park. We did notice that if several families were traveling together they tended to congregate at one site for dinner then go back to their respective sites. Unless someone was unruly, I don't think anyone noticed or cared. We had a group behind us that seemed large, but I didn't count or know that there was a limit. As long as they did not spill over onto my site and were reasonably well behaved I didn't care. Go, have fun and don't worry about the extra person.
