My mom is in a controlling abusive relationship

My mom will not leave her husband because she says its not that easy to just leave which I understand it's not easy at all. But in the past he has domestically abused her, verbally and emotionally abused her. They get in screaming arguments almost every day. She complains and says how much she wants to get a divorce every day. My sister and I cant even talk about our biological dad around him because it makes him jealous/angry and he will start an argument. He also will yell at her if she spends too much money.

Well now apparently he is tracking the mileage on her car to see how far she is travelling which is extremely troubling to me? Idk why no one else is taking this serious. How would you convince your mom to leave?