Help. Worried about my mom

So my mom has been with my step dad for about 7 years. I always thought he was a bit off but everyone told me her happiness was all that mattered even if i didnt like him. The past 4 years however have been awful for my mom. She gave birth to my baby twin sisters, which led to her having internal bleeding and needing a hysterectomy, which led to two strokes and her needing heart surgery, which has now led to a terminal illness. He and my step dad have been miserable during this whole time. He treats her awfully. He gives her a small allowance of 1500$ a month for groceries, yells at her any time she buys herself anything and reminds her he wont be giving her any more money, her car is broke down but he wont get her a new one (even though he bought himself one) and wont let her drive that one so shes stuck to going to wherever she can walk to with twins (which if you can imagine isn't very far) He calls her a bitch all the time and is extremely controlling. He has hacked into her phone so he can see what she looks at, has opened her mail, and is now considering working from home so he can keep an eye in her. She wants to leave him but becausr of her strict allowance theres no room for her to save any money and she has to feed my baby sisters, and even if she had the money she cant go anywhere because her car is broken. I'm in college right now, and dont have a job to give her any money. I'm worrries about her and it breaks my heart to see her living the last couple years of her life this way. She's depressed and miserable. Does anyone by any chance know what i could do to help her? We are both lost on what she can do but I refuse to let her feel helpless