A parents favourite

I live with both my parents. my mom has a mental disorder, dad's a doctor. I am a young lady and I have 2 brothers. My parents favor 1 of them the second born. He has openly admitted that my parents have confessed he is the favourite out of all children. I don't have a problem with this. I cannot make my parent love me more. But the problem lies.... The golden boy has spent the past couple of years reporting his side of the story to parents e.g when he bully's my younger on or when he misbehaves and I try to correct him. He constantly leaves out parts where he lies manipulates uses violence and others when doing so and the had started to paint us (esp me) as bullies to him in my parents eyes. I would get blamed scolded and punished for things that were not my fault. And finally today I chose to speak up. My father said he and my brother are allowed to beat me and shout as they please. This hurt a lot. In the past I knew that there would be unfair treatment against a girl child but I never expected it from my father! In the past I've had bag of food thrown at me and constantly told that I should never correct the golden boy when he does something wrong like fight with his brother. I've been called names stemming from untrue stories. I have been beaten and kicked for unreasonable things e.g quote "ruining my parents marriage" like as if I told one them to cheat, I was just a couple of months old. I've had moment's when my mother put a knife to my throat and told me she would end me. I thought she was joking and would do it. I felt touch my skin and start to slice and I fought her off.