All of these questions are now on the table in our culture

Marriage: it’s time to clear away the fog

Can a man marry a man? Can a woman marry a woman? Can a man simultaneously marry several women, or a woman several men? Can a man simultaneously marry several men, or a woman several women? Can a man marry his sister or his mother? His brother or his father? Can a woman marry her brother or father? Her sister or mother?

http://www.catholicherald.co.uk/features/2012/03/07/marriage-it%E2%80%99s-time-to-clear-away-the-fog/