I think walking away is the best option, to be honest. I don't think I've responded to you before, but I have been reading your posts. You have given all that you have, and more to your father, and it's not enough for him. It will never be enough for him and you are going to end up broken.
Step right back - stay away - look after yourself and your family.
My suggestion is that you take at least one week, ideally longer, with no contact at all. Then set a limit - maybe a 15 minute visit twice a week, and if he's unpleasant to you, get up and leave. Don't do his washing, don't take in any food. He is in a care home - he is being looked after.
Pay attention to what your DM said to you.
Take good care of yourself. Walk away.