17. Not Weird At All
This was Mexico back in the day, and I’m not quite sure how different it was over there a few generations ago, but my great-great “grandmother” was unable to have children. Apparently, my grandfather was told that because of this, his “aunts” gave his “mom” their children occasionally.
What really happened: The wife was unable to get pregnant so great-grandfather had slept with the wife’s sisters and took the children when they were born. Apparently, this was completely normal and no one cared.