Advice????

My brother and his wife are acting childish. They fight over everything! They live in SC and CPS is really strict over there. Anyways they always argue and then my SIL calls me crying  and wanting help and telling me that if he doesn't stop cussing at her and being mean she'll divorce him yada yada yada but never blames herself for anything always him. She so caught up in her work staying until 1/2am at the mall where she works and she talks down to my brother, who isn't perfect, but he's still a good person. My brother has always had a temper even when we were younger. He is now a military vet, 2 tours overseas, killed many people, and seen many of his buddies killed. He gone through some tough shit. And when he calls me upset telling me that she talks to him like he's dumb of it makes me mad. So when they get in a fight I always have to hear both sides of the story to make sure nothing is different. Just like when kids fight. But they have a daughter and when they argue it's always in front of her. My brother and SIL don't know how to handle their shit. They are 21 & 25 and are still calling my mom and I griping about one another. Idk how to help them anymore I'm in Texas they are in South Carolina. They won't go to marriage counciling It's kind of sad they are asking me and I'm the younger sibling. What else  can I do to help them out????