Anybody have experience with how to deal with hoarding and irresponsibility?

What kind of POA do you have? Does it require that mom be declared incompetent by two doctors? If mom is still competent, she can change POA to whomever she likes.

Hoarding is a mental illness. Does mom receive treatment for this? Have you spoken to her healthcare provider in the past about this issue?

If you disagree with mother and sister's way of living, perhaps walking away would be a hard choice you need to make.

You are fighting two people, not one, so you are outnumbered. If the money your mother receives comes from the State and not from you, then my advice is to step back from managing your mother's affairs until your sister is out of the frame. It will be easier to extricate your mum with medical help if she can be accommodated in full residential care.
That leaves her house and the hoarding daughter.
Questions to raise - who owns the home? Did your mother ever make a will? Does your mother have a lawyer whom you can trust? Does your sister have any income of her own? Has she exercised any right to stay in the home that she has cluttered up?

If residential care would require the sale of the home and its contents in order to provide the budget for the care, then this should be handled not by you directly but by your lawyer.

If your mother is competent, she is entitled to revoke her existing POA and create a new one appointing whomever she pleases.

Until you have established that she is legally incompetent, you can't do anything against her wishes.

Are you sure you especially want this job? The job is to manage your mother's affairs #1 in her best interests and #2 according to her established preferences. Sounds like you're not so keen on Item 2.

Freeze your mom's credit.

Only money that should be getting spent is on mom's care. Not house. Not utilities. Not sister.

forgot to mention mom is in board and care. 100% paralysed left side, cant eat, toilet, or move herself. House insurance lapsed and uninsureable or livable state. They say "ok saving money and lot cant burn down-deal with that when it happens". No answer for "where would you live?". Trying to stop bleeding of money for her needs. Yet just today sister tried taking out credit card in her name. sister 2 has $50k loans in her name and tries get more to make min payments on others. only reason not more loans is they ruined her credit so bad, get rejected. Really poor financial logic too. Have 3 refrigerators filled with rotting food cant use costing $300/mo. Solution - install solar panels for $50k. I walked away before and this is what happens. I don't want to do this, easy thing is walk away, but conscience would haunt me. Dont know if can consider mom mentally competent based on decisions made or neglected more accurately.

I need to confirm my POA is "durable" and still active as got it 20 years ago after father passed but really dont use it.

Suggested we all seek hoarding treatment they refused saying they don't have problem. Believe me they do - my GF refused to stay in or even visit house since we both got sick trying clean up only to have them pull junk back out of trash and reclutter - never toss, sell, or recycle anything only accumulate and never clean. oh 4 cats 2 dogs are more important than anything.

So your mother is in care, and realistically is likely to remain so.

Your sister meanwhile is still living in your mother's house. The house insurance has been allowed to lapse. Yet it is overstuffed with consumer goods and has - ? recently? - been fitted with a solar energy system.

Presumably your plan is to sell your mother's house and draw on the proceeds to fund her care. Even if your mother does have enough money to do without this capital, it is still your responsibility to manage her income and assets as efficiently as possible.

You can't sell the house when it's got a sitting tenant in it.

So you have to remove the sitting tenant and have the house made saleable.

Your mother will not consent to this unless and until your sister has somewhere else to go. No matter how deeply you have come to loathe your sister, and however good your reasons, your mother does not feel the same.

So what are you going to do about her? What are her needs, and how can she be helped to meet them without these continuing raids on your mother? - not financial raids, which you can probably put a stop to comparatively easily, but emotional raids.

How long has your sister been your mother's live-in caregiver? Will she have acquired rights of tenancy? Was there any kind of financial agreement between them?

At 89, post stroke and with heart disease, without wishing to be cruel, it seems likely that your mother's death will mean that sister will be independent before very long whether she likes it or not. If you don't want to help your sister, and who could blame you, who else might? Does she have identified problems that prevent her from becoming a normally self-sustaining functioning adult?

Is there a mortgage on the house? Or worse, a reverse mortgage? In either case, lack of insurance will have consequences.

Have you talked to an Eldercare attorney? As CM points out, sister may have rights of tenancy due to caregiving.