The problem that the new idea of marriage presents is that one can not be married to one's sister or any of the עריות (the sexual relations brought is Leviticus). Man lying with a man is one of them. In fact, the death penalty is attached to that act if done on purpose,- and if by accident, then a sin offering.

I mean to say that even if one would actual try to marry one's sister or mother, the marriage is not valid. People might call it "marriage" but that does not make it so.