This story, OP, resonates with me as my own DS did the same when my DM had Alzheimer's and was in residential care. She accused me of leaving her to do the 'lion's share' of visiting etc. when she moved mum from being equidistant from both of us to within five minutes' walk of herself.
We could hardly fit in weekly visits when the car journeys took all day and, when, often, my DS did not offer us so much as a cup of tea when we were so far from home.
My Ds stonewalled, kept vital information about mum from us and was generally witholding so making impossible the demands she also placed on us to help.
I have no advice to offer. When communications break down it becomes impossible. Others think blame for difficulties lies on both parties and in our case it was the ill will of my DS which drove all the problems. It seems to be the case for you too. Having the moral high ground is of little comfort when you are under attack.
But you have my heartfelt sympathy.
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