His Muslim wife’s relatives are kaafirs who mistreat her

I'm in very close family they are there when you need help they're very supportive of me. My wife family isn't close to her at all nor are they close to our kids.My wife brothers talks to her as she are garbage, they cheat her out of her money by telling her lies of deciet, they drink, and commit adultery, and her sisters on the other hand threaten her a lot by calling "DCFS," they call her liers about everything, they disregard everything she say, and they have gatherings and she's not invited, and they all hate Islam and talks negative about it.Where do draw the line and say enough is enough. I know Islam teaches us to be kind to our family members but how do you deal with family that don't respect you and criticize you all the time. My wife get angry at me when I tell her about them, even though she knows how they are. What makes me very angry is that my wife brothers say things to her and she makes excuses for them about why they treat her this way that if I were to say similar she would blow the roof off the house,and if I asked them why they talk to her that way she would accuse me of making fitna. How do I deal with matter or how should she deal with matter. please advise