The composite has Mars sqquare saturn..
That denotes violence in the relationship. I think harsh aspects to mars in a composite are not favorable.
Also their sun semisquaring each others' sun leads to the argumentative nature.
If she isn't safe, she needs to move out for a while. Even if they attempt to work on it and stay. For now she should move out to a safer place.
When a man hits a woman, it's a stron power play. He thinks of her as an inferior in some manner. He looks down upon her. Because imagine if he respected her or thought she was far superior to him? He would be scare to touch her for fear she would leave him.
He's grown complacent. If your sister tries to hold on more in his eyes, she'll be viewed on as weak....very weak. He won't value her as an equal. This is the business minded/ political power play that goes on in most relationships.
Every woman needs to have a few cards in her hand. IF she hands them all over, she'll also get run over.
Keep your sister out of harms way. Don't tell her that her husband might beat her up etc etc. Generally people don't like hearing that their love life is a mess, even if they recognize the same. Just tell her that *you* need someone to stay over to keep you company. Or have someone else close to her make that excuse. Keep her safe. Give her time to reflect and gain new perspective.