I take a different perspective, though similar, to the others here. You seem to have given all the power over yourself to your wife and sister. It almost seems like it's your responsibility to take care of both of them and assure that everyone is happy.

That's not your job! ultimately, they each need to take care of themselves, and you need to take care of your self as well. This doesn't mean pushing either your wife or sister away (though they may try to make you feel like you are). Ultimately, if either is moving away, it's not because you are pushing them... they are making the choice to move away from you.

There is no reason to be caught in the middle of this. Your sister can say and do as she pleases, and the same for your wife. Just be there to support and love them both. If one or both of them want to blame you or accuse you of taking sides, that's their choice, but you don't need to take that responsibility onto yourself.