you asked for advice, didn't get one you liked and put them on ignore...well ok I guess i'll probably end there too.

had the similar situation with my parent. my siblings decided they wanted nothing to do with my mother. she had dementia, was incontinent and was pretty much even more vile then she was before. they fled never to be seen again. I got stuck with mom. care 24/7 plus working full time. basically the only way to get her into a care facility was to walk away & let the county come & care for her because she was neglected.

you are lucky, sister is power of attorney. leave everything to her. let her bear the brunt of it all. don't involve the kids it isn't fair or right to do so. nothing they can or should do about it. if you don't like what the sister is doing, my basic option for you is to leave & let the sister deal with it. mother will eventually end up in care facility because sister won't care for her. period. as I said you are lucky. sister by being POA has decided whether she realizes it or not to handle everything. find another place to live & be good with it. this could go one for years and get even uglier.