How do we as a family come together to help our mother age in place after our mother gets dementia and turns nasty and refuses care?

You need to get Mom to a Neurologist to get a formal diagnosis of Dementia and the type. Different meds work different on different Dementias. When you do this, then you ask for a medication to help with the nastiness.

When you have a formal diagnosis, check ur POA to see how many doctors are needed for diagnosis, your POA is now in effect unless you have an immediate one. Then you have to tell yourself, I am the POA and the final decisions are mine. You must be willing to take the heat. The brother 9 hours away has no idea what is going on. Your Dad was probably able to cover up alot when it came to Mom. Now you see how bad things really are.

Its no longer what she wants, its what she needs. Depending on where she is in her Dementia, you may want to sit her down and tell her if she wants to stay in her home, then she needs to except help and be nice about it. I am not beyond a little threat. Also tell her if she doesn't allow help then the State could come in and take over her care and they will not allow her to stay in her home. She will be placed somewhere of their choosing.

Dementia is so unpredictable and there is no rhyme or reason to it. In the early stages the person loses the ability to reason. Short-term memory is lost. And eventually longterm goes too. They become like small children. They go back in time. This all falls on you and because of that you need to take you into consideration too. You need to ignore this brother even going as far as blocking him or not answering the calls. Mom assigned you her POA for a reason. Your responsibility is not to do the physical care but to keep her safe and if that means an AL or LTC then so be it. To spend her money on her and her care. When its gone, then you apply for Medicaid. Never use your own money if u can help it. Get siblings to help in that area. You should also keep good records. For me, Moms bank statement was my record. A check was written for everything to do with Mom. You saw the money coming in and going out. My bank, for a fee, has copies of my check printed on my statement. If I bought something out of pocket, I reimbursed myself once a month by check and kept the receipts for that month in an envelope with the ck# on it. I will bet the brother 9 hrs away will one day question your spending.

Mom will not be able to stay in her home forever. She will need 24/7 care that may go beyond what you want or can do. With u 2 hrs away, what you are now doing for her is going to become too much for you with running 2 businesses. You are going to start, if not already, feeling resentment. Your best choice would be to get her in a nice AL near you. Do what is best for you. If brother thinks he knows best, tell him he can take over and walk away.

The caregiving arrangement needs to work for both the receiver and the giver. Right now the receiver, your mother, has dementia and in no way should be calling any shots since she is making your "job" onerous and is no longer operating within the bounds of reason and logic. Your brother, if he doesn't have any legal authority in this situation, needs to be reminded that his constructive input is fine but he doesn't get to determine the ultimate care plan for your mom if it creates an extra burden for you.

The biggest problem here isn't your brother, it is your uncooperative mother -- assuming that your PoA authority is now active per the requirements stated in the PoA document. If you don't know what that is, please read the doc today. If there needs to be 1 or more medical diagnosis of impairment, and she has this -- you are over one big hurdle.

If there are no medical diagnosis, this is a problem if you can't get her in for an appointment. You can make the appointment for her and use a "therapeutic fib" to get her to her doctor. Then discretely hand then a note outlining you are her PoA and she is exhibiting XX behaviors so please give her a cognitive/memory exam and test her for a UTI. At this same appointment ask for the Medical Representative form (HIPAA form) and have her write in your name and then she signs it and then her doctor at that clinic can disclose her medical results to you without needing her permission or presence. This is what I did for my MIL. The staff is usually happy to help you.

If none of this seems do-able then I would consider resigning the PoA and telling your brother she is all his, and let the chips fall where they may. Both of you will have to watch the train wreck happen and wait for APS to acquire guardianship. Then she will finally get the care and protection she needs, legally.

If you have 2 people fighting you, your burnout is imminent because "helping" or "managing" will be 100% unproductive. Please read other posts on this forum regarding uncooperative LOs.

Turn everything over to the brother and walk away with the door left partly open. It will not change until the power struggle becomes between two not 3. Tell brother to handle this because you cannot physically or emotionally make good decisions (I know, lie, but it is a lie with truth in it). It will be terrible to watch, but sometimes it has to hit the fan before it gets better. Just have a game plan ready when it all starts to unravel. Sometimes the anger is directed at the safe person, keep that in mind. You may need to contact a social worker or discuss this with her doctor.
It is so hard to be the realist in a family situation. Call local elder care support for help.

I'm confused because you say your brother works against your mother's wishes but that he is a "teammate" with your mother. If she really has sided with your brother in the decision-making I'd just step back and turn your POA and Health care POA over to him. You aren't her guardian so you can't impose your wishes on her. You will see that this will result in a crisis that you are trying to avoid but sometimes it takes that crisis to get things resolved.

Only you can decide how long you are willing to/can provide this care. For me, I personally could not. I am so sorry. There is so little else we can say. It will not change in all likelihood, and will only become more tough to do. We all are human beings, not gods. We all have our limitations. For all intent and purpose, who your Mom was no longer really exists (or if she was already always this way, I fail to see why anyone would sacrifice themselves; it is again an individual decision).
I sure do wish you the very best in these tough times.