Problems with the In laws...help!?

I've got this horrible problem. My wife won't stand up to her mother or anyone in her family regarding her marriage or family. Her mother says the nastiest things sometimes and spoils children rotten to the point where she undermines us when we tell her not to do it. My wife does nothing. Even her brothers disrespect her and take shots at the marriage. she does nothing saying well maybe they are upset over something else. I blew my lid after about the 1,000th time telling her if you don't defend us it eats at the foundation of the marriage what next? I'm furious at her for not listening to me and now because of it i dont feel the same way about her and feel like she's disloyal to the marriage because she won't defend it to anyone.