Need advice for care decisions regarding my mom while navigate relationships with siblings.

Good afternoon fellow caregivers. I have DPOA over my mother's legal and financial affairs and have exercised this power for about two years, since Mom was diagnosed with dementia. I pay her bills, consult with her attorney and financial advisor and accountant, bring her to many, many appointments with doctor, dentist, etc. I am also the alternate health care proxy if my brother is unable or unwilling to act as the primary HCP. My older sister has successor DPOA. My mother made these decisions many years ago and I had no input. On July 4 of this year OS visited Mom for an overnight stay at the AL facility where Mom now lives. OS has a long drive and AL provides a guest room for visitors. I live 10 minutes from Mom. Something set Mom off that morning, maybe that she couldn't have the car keys, and OS called me and told me Mom was sitting in her favorite chair and screaming at the top of her lungs and threatening to bite OS. I drove to AL facility and I had never seen Mom in this condition. We spoke with LPN in charge and agreed Mom had to be evaluated immediately. I had to work that day so OS followed ambulance to the ER. The staff managed to take a urine sample which showed a UTI. Mom was still screaming and trying to get off the cot. No restraints needed, thank goodness but ER provided sitters to stay with mom during her stay. ERs are absolutely no place for an 85-year old woman with dementia, and my sister and I asked for a bed several times. Mom received antibiotics through IV, but the infection did not clear for four days. So Mom was on a hospital bed in the corridor of a very busy ER for four days and she was not admitted to the hospital. I stayed with her several hours on F, Sa and Sunday but at least she was receiving treatment for what could have become a much more serious condition. I know some people reading this may ask how on earth we could have kept Mom in a corridor for such a long time, but please believe me when I say how busy the ER was, and it was hard to flag anybody for information. Brother did not come and younger sister was visiting friends in the western part of the state. YS did come to hospital Monday morning and my siblings and I agreed to a discharge, although hospital staff wanted to keep mom longer. She was released and her doctor prescribed a daily antibiotic to prevent UTIs. Now - my dilemma. YS is trying to persuade mom to drop me as alternate HCP and appoint YS instead, because, YS claims, I exercised poor judgment and was irresponsible as I did not get mom discharged sooner. Mom made her choices for POA and HCP when she was of sound mind, and I believe she no longer has the capacity to make changes to these legal documents. I will tell mom's attorney about these events. YS has also raised questions about my role as agent for mom. She frequently asks if mom's bills are being paid in a timely manner. Yes, they are. YS is a bully, and Mom does not need this aggravation and neither do I. I have thought of notifying PCP or her neurologist and asking if they can determine whether Mom is still capable of changing HCP or POA. I apologize for this very long question, but people have offered sound advice and suggestions in the past, and I ask for the same now. BTW, YS did not see or hear mom as she was screaming and swearing and threatening people. OS and I did. God do I hate this whole situation. I watch my dear mother losing so much of the person she used to be. But I just spoke with her and told her I love her.