You raise a lot of issues, and you shouldn't feel guilty about the way you feel. It's natural to feel resentment in the circumstances you describe. I remember hearing Joyce Meyer talk about needing to take care of her parents, who had so badly abused her when she was growing up. I brought my mother who has dementia to live with me, and I sometimes feel resentful even though she was a wonderful mother. All you can do is cross that bridge when you get to it. You will probably know at the time what needs to be done, both for your parents and yourself.