Firstly, make sure there’s really no way you can move out. Is there a sympathetic relative who would take you in, or a friend whose parents would let you live with them for a while? You CAN get emancipated (in the US) if you really try, and it sounds like you’re in a bad spot.
If you really can’t move out, then there are a few things that you can do to mitigate what you’re experiencing.
Firstly, remember that you are not being ungrateful, you are being abused. You do not have to feel guilty.
Secondly, open a bank account in just your name if you can. This is where you should put all the money you get from babysitting and otherwise.
Also, document instances of abuse if you can, and keep it in a secret place, in case you need to bring it to the authorities.
Finally, move out as soon as is viable.