How do I regain control of my own life, while trying to care for and protect my Mom from my siblings?

I'm the youngest child of my parents by 9 and 7 years of 3 siblings. Our mother was physically abusive throughout our childhood. My siblings took her physical abuse and carried the damages into their adulthood. I fought back as soon as I was old enough - not always coming out on top, but she knew I was there and have sought therapy to deal with the abuse and be certain it did not carry on in my children's lives.. Now, my siblings are not only jealous of "the baby," but also the fact that I don't carry the garbage from my childhood as they do (and have handed down to their own children). Now Mom is 90 and has dementia. After caring for her and my Dad for the past several years with little assistance from either sibling, they have ingratiated themselves in her life now, knowing these are the final years of her life.. All of us have borrowed money from her, but I'm the only one that repaid the loan in full and have documentation to prove this. Now that Mom can no longer remember the money they owe her, they have no intention of paying her back. I was POA and Guardian for both parents until Dad passed in 2009 and Mom felt it more "fair" to name my sister and I Co-POA and Co-Guardian (our brother lives out of state). Every decision I make regarding Mom's care is challenged and each week I find something else they've done behind my back. Instead of taking the best care of Mom, their jealousy of me results in them making choices to sabotage the care I arrange for her. I've worked 24 years in the medical profession and know many physicians and can, therefore, arrange for Mom to have the best medical care. My siblings are not appreciative of this perk and are more determined to find a physician that I do not know, regardless of their lack of credentials. It feels as though they spend the weekend thinking up the next wave of drama they can insert into our lives. On top of Mom's progressing dementia, she feels guilty about her abuse during our childhood. They have been distant for many years until her dementia and they found out we will receive a nice inheritance when she passes. She is so happy to have them in her life now and, with the dementia as well, can be talked into almost anything they want. I don't know how to protect her from their selfishness and bring back some sanity in my own life. On Sunday evenings I begin dreading the week ahead and the drama they have planned for the next week. I need to honor the promise I made my Dad to care for Mom regardless of how hard or painful it became, but I now look forward to the time when I can remove these two from my life. When my Mom passes I will be burying my entire family and not just my Mom. In the meantime, how do I regain control of MY life and sanity? I feel like I'm whining, but until I found this site, there was no where to vent and share my story.