My Mom Keeps Misplacing Things & Thinking My Late Dad Is Still Alive

My mom has a UTI (urinary tract infection) that is causing dementia symptoms. For the past month and a half, she's been misplacing things and then blaming it on my late Dad and insisting he is alive and messing with her. He's been dead for more than a decade, but she never came to terms with it. She was taking meds for the UTI, but has finished the prescribed dosage. Now, my older sister (who lives out of state) and I have been trying to keep her hydrated to further allievate the dementia symptoms but she won't listen to us most of the time.

Now, she's been trying to sell the house that I live in with her and cash in her life insurance and use the money to return to her home country of Vietnam. She hasn't been successful yet, but my older sister and I are exasperated. We also have another sibling, but he hasn't been helpful much (he has a complicated relationship w our mom and so do I). He lives in the same state as me, but far from me.

I don't drive but I've been my mom's primary caregiver for more than a decade (from ages 22-34) and I've done the best I can for her. So has my sister as a long distance caregiver who visits once a month.

We have POA, but no official dementia diagnosis yet (though we hope to get it when my sister visits at the end of the month). In the meantime, I would like advice on how to better deal with my mom besides not arguing with her.