I have been working for a couple since 1990. The husband passed in 2008. The spouse is still living, but she does have dementia. I have always taken care of the house and cook. Now I do all of this and more, and I love my employer. I did like my job, but now I hate it there. Reason why, is the greedy daughters. I really am thinking about reporting them to APS.
They have become comfortable knowing you have been there since 1990 and they may not even realize the changes in their own Mother. In their eyes they are doing the best for their Mother because they know you are there to care for her.
If they are doing something abusive to their Mother then definitely report them if you feel you need to.
I think a discussion with the family is needed and you may need some time off to think about what you may need for yourself. You must be so burnt out
The question is whether they're doing anything that is bad for your employer, or only disgusting you by their attitude.