Probably not like... 50, but even in a small town of a couple of thousand people, you're going to be interacting with 1st, second, and third cousins pretty regularly. I have a friend from an old family in a small modern town of 15k, and she said that dating in highschool was actually kinda fraught because of this.

I think that level of incest is actually way more common than our modern sensibilities would suggest. It isn't siblings fucking or anything.