What can I do when my father’s heath directions were not followed by either my mother or my brother?

I have just discovered that my father's directives regarding his illness were not followed by my mother or my brother, who acted as his doctor. I do not know how to handle this because my father suffered so much for so long. I was left with the cards and papers that are often present at the end of someone's funeral. I started organizing them today after almost a year since the funeral and stumbled upon the full version of my father's POA. I had only seen part of it during his almost year long illness. This was legal and signed, my mother and brother had copies, but they did not follow it. Dad asked to be allowed to die peacefully if everything had been done for him and he was not going to ever recover any quality of life. Every doctor except my brother kept telling us he was suffering and would not recover from his two strokes even though he was mentally alert. He could not live without the vent and went through attempt after attempt when people tried to wean him from the vent but he could only last for 3 days at the most before crashing again. He actually grabbed my shirt once and told me to tell the rest of my family that he wanted nothing else done. My brother and adult nephew told me he did not mean it. In the end, Dad's case worker at the hospital my brother worked at came to me and said no one else would make a decision, my brother was about to be called before an ethics board, and my mother needed to meet with her. My mother told her she was too busy. Ironically, this all took place on the day my father told me I had to make the others, much older and rarely present, let him die. He told me I was strong and tough enough to do so. The caseworker and I found him another placement and he died within three weeks. I have been haunted by all of this. My siblings were so ugly to me throughout the time Dad was ill because the health staff at the 9 facilities he was at saw me daily and told me the truth. I tried to tell my family the truth and they didn't want to hear it. My brother has always been my hero but he has admitted to me that he shouldn't have been so involved with Dad's care. Each facility told him so and he created problems. My father died holding my hand with none of the rest of my large family present. I did what he wanted, but I am battered and heartbroken that he was allowed to suffer. How do I ever handle what happened to him? I appear to be a gentle, quiet special education teacher, but like most teachers I have learned to deal with tough and heartbreaking situations. My siblings and I are far apart in age and location. We really don't know one another. They partied throughout my father's illness in hotel rooms while my mother continued with her interests. My husband, teenage son, and I looked after my father. How do you handle information like this? I can't change my father's suffering nor do I want to be hostile toward anyone. I am too tired and sad.