My mother raised someone else kid with my father

I 25(M) recently discovered that out of 3 siblings i have one of my sister 21(M) is not my father’s. I knew about this that my mother is cheating on my father with some guy just that I didn’t had guts to confront her. I moved to bangalore away from my hometown UP and got proof of her cheating, couldn’t believe it so I directly confronted her, she flipped on me on call and said she will file police case against me and tried threatening me. I have few call recordings of her arguing with me on this topic. Since the day I told her that I know everything, she started running bad mouth about me to my other siblings. My father is a wise old man and is not aware about this, I feel he has the right to know about this but I don’t know what to do in this situation.
The guy she cheated on is filthy rich, I was soo much stressed with this that I thought I can take my exit from all this and blackmail that guy to give me some settlement money and I can exit the country starting a new life away from all this. My middle sister who is my step sister also aware about this now but she flips on me telling let it be like that.

I don’t know what to do here but one thing that I have in my mind is that I want to take a exit from all this, because I tried to explain her this wrong and tried to rescue her but she tells what she did is correct and doesn’t want the chance.

It’s been an year I haven’t been home and my father keeps calling and asking when I’ll be back.

Location: bangalore