Stress that WILL kill you. 😭 advice?

My mom is a wonderful person, although we have struggled hard in the past. I moved out at 16 and currently 19 still living on my own. Well I have a sister who is about to turn 21 and living with my mom still and she has a 1 year old daughter whom my mother has cared for since day once. As my sister and her ex use to sell and do cocaine, so my mother is now the adoptive mom. Well anyway, my mom has struggled hard in the past with illnesses, from breast cancer to a throat tumor to a slipped disc in her back and now the dangers of a heart attack she was just hospitalized 2 days ago for that, and it's all due to stress . She works hard everyday for social services helping the mentally ill and still manages to care for my niece and my sister, all while struggling really hard to pay bills. Well my sister doesn't work, she doesn't care for her own child she sits on the couch all day, doing nothing! She drinks all the booze my mom buys (in which my mom is now trying to quit drinking ) she eats all the food as well and doesn't even help clean the house. She won't even work with social services to try and find a job so she can get money from them, where ever the small amount of money she has goes to her, piercings, parties, clothes. nothing that actually helps out my mom, I have told my mom countless times to tell her to get off her ass and get a job or move out but still no change. the stress is seriously going to kill my mom and my sister doesn't care, she is a child at heart. I feel so bad for my mom and what she has to deal with, I wish I could smack some sense into my sister 😕. I don't know what more I can do except complain, I'm starting to worry about a lot more.. I'm at a loss.. any advice?..