How to deal with anxiety and guilt over not being able to remove impaired medical POA for my elderly mother?

Hi everyone,
First, to all those who are on this often lonely scary journey of caregiving, you are ALL in my prayers. I am so thankful for your stories of hope, courage, and the encouragement you all give to the group members. To those of you who are just starting this journey, may I offer one bit of hard earned wisdom:
If you are asked to help in the caregiving of a loved one, especially with regards to decision making, either take it ALL on (financial AND medical POA) or take on NONE of the decision making, and just love that person and help in some other way. I have served as the financial POA for 10 years or so. Thankfully, my older brother will be taking that over soon. However, we are currently attempting to have my younger sibling removed from healthcare POA duties because, due to his unstable erratic behavior due to end stage alcoholism, he is NOT acting in my mother's best interests, and has fought us every step of the way to help her get appropriate safe care as an Alzheimer’s patient. I have spent money talking to her elder law attorney, her neurologist, hospice staff, etc. to no avail. She is no longer deemed competent to change the designation. She states that "he takes very good care of me" even though he has repeatedly made medical decisions that have put her financial security at risk- withdrawing her from an insurance funded rehab facility after a broken pelvis prematurely. We had to get 24/7 home care which is only minimally covered. My mother has to listen to drunken verbal altercations between he and his wife that go on until the wee hours of the morning, people who alternately ignore her or boss her around. Did I mention they live there rent free and have for 8 years? :( I have been told that these issues are not enough to warrant APS intervention. I have notified her elder law attorney, her medical staff, etc. I cannot move my mother into an ALF because he refuses, and if I upset him, he will remove the home care folks entirely just because he can. She needs them to just have a way to socialize and get out and about when I am not in her home state. I am not in a position to take her to live with me, and she has appropriate resources to go to a very nice ALF- Memory Care facility, but he refuses and gets in a rage at the very suggestion. My momma just wants to keep him happy. I have been told that I have done everything that I can do, and I truly believe that to be the case based on my conversations with her doctor, her attorney, and my colleagues who have worked for APS. So how do I live out the Serenity Prayer over this? I cannot go on like I am. I have never suffered from actual depression or anxiety disorders but as a person with a background in counseling and behavioral health, I recognize the symptoms, and I am truly scared I am falling into that black pit. Thank you for hearing me out. I know that my Redeemer liveth. I know that Jesus is with me and will see me through. But I will happily listen to any of you folks who have come out on the other side of these feelings as well. Thank you and may God bless.