Hi 3joys - welcome to the forum!
It sounds like you are so intensely frustrated after providing support and putting up with verbal abuse for so long.
Its hard to improve a relationship when dealing with really negative behaviors and as a result feeling very negative emotions. For me, detaching from things I can't control and trying to find a place where I feel in control of myself, lets me reduce my negative emotions. I also use the Buddhist meditation to want good for myself and others - Buddhist teachings are actually one of the inspirations for DBT therapy.
The idea of 'radical acceptance' - accepting the current reality as fact, just accepting it, and then also wanting to change it, is another key part of DBT. Reading and learning is a big part for me of being able to calm and find hope and peace. Have you read the links here so far? There are lists also of good books for deeper study, the more you learn then you can focus on sort of professional behavior and trying things to see what works, for me that helps me to focus on myself because that is the one thing I can control!
It may not help them, but we can help ourselves to deal with the situation differently to make it less painful for us as parents - and in the long term that may help the relationship.
Wishing the best for you
