When my mother lived in America she lived next door to a family. The family was made up of two parents and five children. This family was seen as a respectable well liked family in the community.
During the summer, when the parents went out, the oldest son would take the the rest of the children up into the tree house in their back garden and would "teach them," weather they wanted to or not, about sex. He would actually have sexual intercourse with the youngest daughter.
One day two neighbours spotted what was going on and informed the parents. The next day the house was empty and the family had done a runner from the town overnight. It was the scandel of the summer in Mechanisburg.
Ever since hearing that story just thinking about two relatives, even if they're conscenting, performing sexual acts on each other makes me feel rather sick. I guess I'm not as open minded as I thought.