How to get away from JNM

TW: mentions of abuse and s*xual assault

Hello, new user here! I’m looking for some advice on how to escape the abusive relationship I have with my JNM

For background:

I grew up in my grandparents care for about 7-8 years? It all stopped after my grandfather passed away and my mum decided she wanted me back. During this time she was in her home country blowing her money and was like a bank to her family. She lost a lot of money back then and dealt with mental health issues I don’t want to disclose but she’s never gotten the proper help she needed. My brother also grew up with me and I have another brother whose basically like my mother, we did not grow up together.

After I moved back with my mother, all I remember is constant verbal abuse and sometimes physical. On one occasion, she ripped part of my hair out . I also want to add I’ve been SA-ed twice while living with her, by people in her house

I did see my grandmother during holidays but sometimes I wasn’t allowed to. As my grandmother can’t drive she couldn’t come get me herself, I had to wait for someone to arrange it as she did live 2 hours away.

Anyways, after recent abuse I’ve decided I’m going to try live with my grandmother now. I’m going to stay with her tomorrow and I need advice on how to bring up the topic with her, and if she does agree how do I tell my mother about this? How do I tell her I won’t be returning home

I do feel guilty as she is my mother in some messed up way but I know what she is doing is wrong and I want her to get the help she needs. Of course in the future I’d be open to re-amending my relationship with her but right now, no

Also extra information:

-Said grandmother is my dad’s mother. My dads side of the family knows about what shes done to me. The reason nothing has been done until now is because I didn’t tell anyone the full story until a month ago. My grandmother knew but because I was a minor at the time she didn’t want me to go into foster care as horrible things happen there.

-My dad is in the picture, he’s just as bad as her. He’s never be physical but hes been emotionally abusive to me. I have no real memories of him from my childhood which says a lot.

Please don’t share my story anywhere, it’s been really hard for me to open up to my relatives and friends about what I’ve been through. I just need help

edit: I’m sorry I forgot to add I’m from the UK, here its legal for a 16 year old to move out

How to get away from JNM