With the exception of a few historical examples such as Incan, Hawaiian, and ancient Egyptian royalty, incest taboos universally prohibit sexual relations between which members of a group?

parents and children and siblings

Explanation:

Incest I defined as the human sexual activity between closed relatives or family members. Hence I was prohibited and seen as a taboo in so many part of the world. Probably to avoid breeding with the family or to prevent disorderliness.