When you marry someone the one you marry becomes your priority, this is the way it should be. but sometimes when the person that one is married to tends to amplify this to an extreme extent, as frust said, when they have a problem with the in laws.

It may be an unhealthy relationship with her but the truth is it's a tough situation for you because on the one hand you can't really do anything to make him change and on the other hand as you said you feel you're losing a brother.

About the best advice I can give you is this. You've been his sibling (not sure if you're a sister or brother but it doesn't matter), all his life. As the relationship grows more stable (he and his wife's) perhaps he'll come around but in the meantime what you do is cut off the bad treatment of you by not tolerating it. If the only way he interacts with you is with sarcasm, joking and ridicule. Don't put up with it and kindly end the conversation when possible. Walk away. It may mean talking to them less for now but it will send the message that it's not acceptable. If it's in text, end the text conversation by stating matter of fact that the joking is not acceptable and you'll talk to him when he'll be respectable to you again. Phone, same thing. state the same thing and say your good byes. In face to face, walk away if possible. don't make a rant over it, don't do anything drastic just end it and walk away.

No guarantees this works overnight but two things happen. you save yourself the distress of the ridicule escalating your mood in a bad way and you send a message to him and/or her. You'll have less conversations in the meantime but more peace.

Hope this helps.