Forgiving an abusive parent

The article on forgiveness of an abusive parent was full of good advice and wisdom. I care fulltime for my father with dementia, and have for almost 4 years. He is a wonderful, Godly man, and was a precious daddy to me. However, my mother is a different story. They have been married for 63 years, and I have had to insist that my mother stay with my older brother, who lives about an hour and a half away. There is a great deal of resentment towards me regarding "separating" my parents. However, my mother has been a prescription drug addict for my entire life, and growing older has only created more difficulty with that issue, such as falls, sundowners, etc. She and my brothers have lived in denial about this issue, as is common, and they let her take meds freely, irregardless of the dangers to her. My father and I have been the ones to try and help her throughout the years, but at this stage in his dementia, he doesn't realize she isn't here, and when she is here, he becomes upset and cannot sleep (often due to her erratic behavior and falls.) I do suffer some guilt over the fact that she is not living with my dad, because she is not a bad person, just a horrible addict. But I have had to go as far as quitting my job to care for my dad, and get zero help from my mom or brothers. I am only medical POA, and they only give me a stipend of $400 per month to care for him, which provides NO money for breaks nor really anything other than his groceries and personal hygiene items. I have been able to utilize the VA for adult diapers and such, which takes a tremendous load off. Since I quit my job in June to care for him, I am living in their home "for free" (as my family puts it,) but this causes resentment on my part, as while I had my dad in another state while still working, my mother let my brothers' grown children live here and footed the entire bill, though their only problem was not wanting to work. I primarily used my income to support my dad before moving back to my hometown. It's my dad's home, my dad's money that pays utilities, and is keeping my dad out of a nursing home, so the "letting me live here for free" remarks do make me resentful, especially since he is total care. I also know that my brothers are assuming that when my mother is no longer independent, that I will simply become her fulltime caregiver. I cannot live out the rest of my life that way, as her drug addiction reduces me to the emotional level of a small child every time I am around her for any amount of time. There is too much hurt that is ongoing. I have forgiven her for the past, but how does one deal with continuing behavior in an aging parent? I understand that she likely has deep-rooted hurts in her childhood that have driven her to be an addict, but physically caring for my father is breaking my body down. If I take her on, then I feel as though the added physical burden, along with the emotional toll, will literally kill me before my time. When she stayed with me for a year upon initially taking care of my dad, I had such chest pain that I had to have a heart catheterization, and the cardiologist told me that though my vessels were clear, I could easily have a heart attack due to the amount of stress that my mother was causing me. He prescribed anti-anxiety medication and that was the point I had to insist she live with my brother. Though I was very kind to her while she was in my care, she is quite dramatic, and loved the drama that surrounded being sent back to my brother, and has spoken very harshly about me to anyone who will listen ever since. The only way I can cope with that is that I know God, my father (somewhere deep in the recesses of his dementia), my teenage son, and closest friends know that I do not mistreat her, and that I have taken excellent care of my father. Unlike my mother and my brothers, I will have no regrets when he passes, and my conscience will be clear. So...my dilemma is...I cannot emotionally afford to care for her when she requires fulltime caregiving, which is likely not long from now. And I do welcome her to come spend a few days per month with my dad, as again, she does love him deeply, but both my son and I are left with having to deal with recovering from the emotional fallout for several days after her visits. It is scarcely worth the damage it causes each time she comes, but I have to live with my actions, and feel it is the right thing to do to let her spend time with her husband while time is left. Does anyone in the caregiving community suffer any situations similar to this, or have any insightful thoughts to help me cope with this situation? There will be tough decisions in the future that will likely destroy what is left of my family, and that makes me very sad. I'm afraid that with the death of my father will come the death of any remaining family relationships. Thoughts on this situation are welcome and much needed.