I either put my mother (91) in ASL or let her live with her sister (80) 4 hrs away. They want to be together. Advice?

The question is, is an 80 y/o capable of taking care of herself AND a 91 y/o woman with dementia? Can she drive a car and meet the demands your mother will put on her, in addition to meeting her own needs? To me it sounds impossible, to be honest. I wouldn't place a 91 y/o dementia patient with an 80 y/o elder under any circumstances myself, despite the Aunt 'wanting' to care for her sister. "Wanting" to and being "Able" to are two different matters. You'll be 4 hours away, to boot, so if/when the sh*t hits the fan, you'll have to drive down there to clean up the mess. Are you in a position to do that, with cancer to deal with?

I personally think your mother is better off in Assisted Living or Memory Care AL b/c it's not the horror show many people think it is. It's actually a place where teams of caregivers and nurses work 24/7 to manage the care of our loved ones, do activities and socialize, eat meals together and things like that. The elder gets to socialize with other elders in the same position they're in, and together they thrive. They also get their meds on time, doctors come into the facility on a regular basis so their care is overseen by professionals, and that's nothing to slough off! The moment something goes awry with your mother, it'll be noted at the AL and dealt with accordingly. I'm sure my mother would have died long ago had she NOT been in managed care where they noticed her pneumonia immediately on 2 occasions, and also a UTI among other things. A medically supervised environment is preferable for a very elderly senior, in my opinion, to a scenario where two elderly women are alone and trying to manage w/o help.

Wishing you the best of luck, however this turns out. And sending a prayer that your cancer goes into remission soon, too.

The real question is how well your aunt knows your mother.

Actually, wrong. The real question is whether your mother wants to live with your aunt - can we take that for granted?

Anyway. If they have always been very close, seeing one another all the time, and if your aunt has ample support in the way of HCAs, cleaners, delivery and laundry services etc etc, then the idea has legs. But don't allow your aunt to be either sentimental or guilt-ridden about it. How closely has she thought this all through?

An alternative might be to help mother move to aunt’s house for now, on the basis that you will all continue to look at ALs. That solves your own problem immediately, does what they want now and lets them check out whether it’s practical, and gets you all further down the path to a better solution.

Can your aunt physically care for your mom? I understand she has very good intentions but at 80 caring for someone with dementia and will continue to decline is tough.
If it is difficult for you I can imagine being 80 and trying to care for someone with dementia! (I did it in my 50's and 60's and I don't think I could do it again as well as I did)
If they want to be together is there a possibility that they could both go into Assisted Living together? Aunt could care for her sister but she would have help if she needed it.
I think I am leaning to....placing your mom in Memory Care if her sister is not willing to move into Assisted Living with her.

Who is your aunt's PoA? I hope someone is. Without this legal authority no one will be moving her anywhere without her voluntary consent or guardianship. If her mail comes to your home, then your home is her legal residence and you will need to go through the courts and a legal process to evict her if she won't go voluntarily (your state law on this may vary from others, but not by much).

If you are her PoA and she has a diagnosis of dementia and this satisfies the protocol for activating your legal power to act on her behalf, then you do what works for you: transition her into AL local to you. Who is helping her sister? Does she have any children local and willing/able to help her? It may be possible for them to be in the same apartment in AL. This is a compromise solution to consider.

If you can please respond about the PoA question, it would allow us to give you far more appropriate suggestions for your situation.

I think that you know this is a bad idea. My vote goes to ALF, not the aunt.
I am 80.
I am a nurse. I am healthy. I am hale and hearty. BUT I am 80! This is a bad idea. That your Aunt doesn't know it's a bad idea is your worst red flag. So sit with her. If your Aunt recognizes her limitations, that nothing stands between her and a broken hip but one wrong step, and that she is prey to all we are at 80 no matter HOW healthy we are, and if she plans to have in place a good support system of family or caregivers, then this may be worth a try. But what there needs to be is both a plan if this doesn't work (I cannot imagine it will) and a plan if this goes wrong because of the illness or progression of illness by either sister.
I can't imagine this going well. That said I understand that you yourself are up against it now in the fight of your life and need all you get in terms of health. For myself I would place your Mom. Esp. if you are to deal with this when/if it all goes wrong.
I am so sorry and I so wish you the best.