ranting about my life cause I can't afford therapy

rant #1- how it is at home

Ok, so this is a long going thing which I can no longer take keeping to myself. So I have decided to tell you as it will be easier for me.
1. My youngest sister is making me sleep deprived and making me loose my sanity. This all started when quarantine hit in Australia, my two younger sisters found Roblox and got obsessed (note that my younger sister was on it first). She used to be able to sleep when she was told to, but it gradually kept getting later each night until it was nearly always at 1am when she fell asleep.
I am in high school and at the time had to teach my sister's and she never paid attention to me when I was forced to help her with school work. I will make another post about her later.
2. I want to run away. This is related with the first one, but also ties in with my dying relationship with my mother and stepfather. My mother has kept me at home everyday unless it was for school work or a production I am still currently in. She is so demanding to the point that I want to cry but keep it in for my other sister who is a few years younger than me that I am practically raising myself (I am almost 17 ATM). My stepfather has been making sexual references for years, saying how much he wishes I was his girlfriend and for us to go into his room and have some "fun".
But if I went to live with my aunt or grandmother I would have to change schools and never see my current friends again.

This has effected my mental health severely, to the point that I broke down Infront of my mother when her and my stepfather were fighting to each other, using me to hurt the other.

So what should I do?