I was molested by my sister

For years now I have been struggling coping with this tramuatic expierance. When I was six years old at the time my parents were going through a divorce and thankfully now they are back together but at the time I didn't know what was going on. I was forced to live with my mom along with my sister at my grandparents house. Me and my sister have a complicatied relationship, we never really got along with each other because we came from different dads. (Now this is where the sick stuff happens) Sometimes my sister would play online sex games and force me to watch them with her and I was introduced to sex at a early age. One day she tied me up to my grandparents bed and put a phallic object inside me. This continued for a few minutes before my uncle saved me. I didn't initically know that until my sister brung it up again as a joke to me. Now i'm 16 and almost 17 and she since moved out of the house. I have only told a select people this. I have another sister who was unfortantly molested by her brother so I don't know how to bring up to her. I told my mom but I don't think she believes me and i haven't told my dad. As for my other sister, I personally don't believe in hell but if there is one i hope she rots there.