Here are the guidelines:

1) These people have to have been in related *real life* (no on-screen acting relatives, unless they were officially related off-screen). Marriage, adoption, birth. (sleeping together or dating don't count, unless it resulted in the birth of a child, i.e. "bastards" are OK)

2) Nudity: showed nipples, areolae, pubic hair, vulva, anus, more than half ass cheeks. "see thru" clothing that shows above parts clearly OK, as is body paint.

3) Both of the parties must have gone nude in some publicly available forum at some time (not necessarily at the same time).

4) At least one of the parties must have gone nude in a one time publicly available film, teleplay, or movie that is generally considered "mainstream".

5) If 4) is satisfied, I don't care where one or more of the other relatives has gone nude, as long at it was publicly available at some time.