Always knew I didn’t belong

At 25 I became ill and ended up in the hospital. During the course of tests it was accidentally revealed to me by a nurse that my father was not my biological father. After both of my parents repeatedly denying it for months my father finally admitted he wasn’t my dad but any more info would have to come from my mom. He wasn’t willing to give any details due to fear of angering my mother. About 10 years later she finally acknowledges that he’s not my “sperm donor but is my dad and will always be”. She claims to have used a sperm bank because my father is sterile, but have also found out from family members that she was also known to fool around on him. I have spent the last 6 months investigating every lead I can find only to run into dead ends, lies, and people with info unwilling to “hurt anyone’s feelings”. Sadly the couple of people who might know the truth other than my mom and dad are dead. I wasn’t raised by my parents either, which makes this whole issue worse. My father’s parents raised me from 18 months old when I was taken away from them by the state after a severe head trauma they couldn’t explain. They received custody of me back after my grandparents passed away when I was 15. We had all moved to another state by then and the new state was unaware of the previous abuse. The rumor around my family has always been that one of my parents threw me against a wall, they still deny doing anything to hurt me. So for either of them to argue the point of “you were so wanted we would do anything to have you” than why did you try to kill me?
I have ended all contact with my parents, siblings, and extended family until I get the whole truth.
So, to my parents I have this to say: In spite of you I have made a wonderful life for myself with my husband. I have the only family I ever needed. I always felt like my “Real Parents” died when I was 15 anyways so no huge loss losing you two again. And waiting until i’m 35 to acknowledge anything was cruel and inhumane.