This topic has come up before and at the risk of repeating myself, I will just say that if any such law is passed, it won't be long before someone is suing some unfortunate priest/rabbi/ minister for refusing to carry out a religious marriage ceremony against his or her conscience. I'm all in favour of egalitarianism in the matter of civil rights but it seems to me that having a religious ceremony when you get hitched isn't a civil right. If you want a religious knees-up after a legal and secular ceremony, what's to stop you organising your own? And why does that need legislation?
Parents-in-Law. What do/did you call them?