No, Darren, I don't think they have. Nowhere does it say by law that it should be only a gay COUPLE that's UNRELATED is the only type of "marriage" allowed along with heterosexual COUPLES but NOT couples that are related...
You can post stories of how relatives shouldn't have conceived, but is an empty argument if you don't also ban traditional couples that are knowingly at risk to give birth to children with genetic disorders such as Downs Syndrome. Both sets of described couples yield a high risk of birthing children with medical disadvantages. You can't have your cake and eat it, too...
Very well Tuttle8....whatever you and your sister want to do...more power to ya!!!