Here is my two cents of advice, coming from another baby boomer - hey, that was a very good thing once upon a time:)
What you can do right now:
1.Quick - easy and so worth it: Get the GoodRX app (both for info about the meds (they also have an online presence) and to find the best price on the meds) - saves you serious money.
2. Go on line and look up ssa.gov and set up an on line account right now for each one of the moms. It is not difficult to do and once set up you can go back in anytime.
3. The account at the soc sec site will tell you everything you need to know, how many years worked and what payments to expect etc.
4. Then call SSA with your questions - you might have to call a few times and yes you have to wait forever, but you will get solid, valid information, so you no longer have to guess.
5. Is there a possibility that either Mom could collect either survivor Social Security from their husbands death or perhaps be eligible under their husbands SS? If there is, make an appointment at the SS office and they'll have money coming in six weeks later. (I had not even known that I could do that, got over $1600 mo and Medicare coverage just like that, all done and first payment within two weeks) Of course, once I looked into it, I made sure I had all my papers and information with me and it was all set up in one appointment.
6. Keep the house, until you have more information. It sounds like a good investment possibility as long as it is structurally sound or all things considered an easy enough fix. That is when a professional opinion is essential.
7. Tell the other Mama that ten years is plenty of time to plan her future retirement. There are still plenty of opportunities for her to stash some cash, find a side gig, rent a room whatever it takes. Time to start kicking butt - some of this is so easy, it only becomes complicated once you are ill.
Sorry to hear you have your hands full, but I can tell you from experience, if you keep on looking for information and solutions you will make it happen. I went through something similar with my mother who was extremely difficult to deal with. She's 87 and she was no fun to deal with, didn't help that she lives overseas and there was plenty of family drama I assure you:)
It is not right that one mom is eating up everyones resources and in all honesty, no one will blame you for feeling resentful. This is/was an entirely preventable situation and I would keep that in mind as you struggle with making it right.
You must look out for your own health and financial well being first or you will be useless to your own family. Treat your own future self with respect - you did it right by living below your means and saving up, which doesn't mean you should give it all up for someone else, family or not.
Lots of good information here, Medicaid might be an immediate, temporary solution, depending on your state at least until she gets her disability. I can only echo that everyone I've ever heard of did not receive their disability in the first attempt. So be prepared to deal with that. There are plenty of lawyers who specialize in that for a fee of course, but it is practically a necessary evil.
Good luck and keep us posted on your progress.