Sister has ruined Mother's home. What can I do?

My sister Jane is in her late 40s and has never had a life, a job, a career, or learned to drive a car. She has done nothing at all to make a life for herself or to be independent. She has always lived with and off my parents. Our father died a few years back. After that, the situation really turned dire over the last several years when my mother finally reached the point where she could no longer take care of things in the home. Since that time, Jane has hoarded every corner of the house. Everything is cluttered and dirty. Flies are flying around. Every surface in the kitchen is covered in dirty containers and trash. There are major septic and plumbing problems, the toilet rocks back and forth over a rotten floor, the water in the bathroom is off because the faucet leaks, the kitchen faucet leaks as well. None of the toilets flush and you have to chuck a bucket of water down them. Everything is dirty and falling apart. You can see where the roof has leaked. Jane will not fix or clean or manage anything. She continues to behave as though she is a dependent child. It's all I can do to get her to arrange doctor appointments and send me shopping lists. Any attempt to address any of the problems results in hysterics, and sulking from my sister. My mother has always been very protective of Jane and feels that she has mental or personality problems. Unfortunately she has compounded the problem over the years by never standing up to my sister and always giving in to emotional blackmail or passive aggressive behavior or hysterics. She says, it's just not worth upsetting Jane. But now, the house has become a horrible, dingy, dirty pit and my mother is basically just stuck in bed listening to music, sewing and pretending the rest of the house doesn't exist. The outside steps and path are slick, falling apart and unsafe. There's barely any space for my mother's walker in the house. All their groceries and whatever else must be delivered by me (I live an hour and a half away) and if my mother needs to see a doctor, I come down and take her there and it is usually an all day affair- especially been Jane comes along. Jane can literally spend five hours trying to buy 10 items, and most of the time, she becomes overwhelmed at some point. This is why I've been encouraging her to send me shopping lists so I can just BRING items. Jane is an extreme recluse who has no friends, never has, and never goes out. She cannot drive and they live out on the country where there is no transportation, not even a taxi or Uber. She seems to live in her own world and gets extremely angry when anyone upsets her reality or suggests that she might benefit by seeing a doctor, a psychologist, or even just a counselor. My mother says it's always easier just to go along with Jane and not risk upsetting her. I feel complicit in all this because I don't know how to proceed, how to change anything. I've told my mother that my doors are wide open and she can come live with me any time she wants. But she is afraid to leave Jane alone. She's afraid that Jane will fall apart. Meanwhile, I realize that I will also be trying to deal with Jane and Jane's self destruction long after our mother passes on and I have no idea what to do for either my mother or my sister. They know no one and have basically exiled themselves into this joyless life. Meanwhile I live an hour and a half away, and I have a very demanding career. I feel the pressure of responsibility every day, but I have no idea what to do. I can't force Jane to get help or see what she refuses to see. But I also can't see my 80 year old mother living in these conditions. What can I do? I worry about this all the time.