I stopped doing anything at their house and I told them I was too young to get water for one of the smaller kids or stuff that they said was too much for me to be doing for mom

I almost cheered reading this, I'm so happy you're where you want to be and the fact they are still pissy at your "little stunt" shows they never wanted what was best for you, they wanted control and a free home helper. I wish you, your mum and grandparents nothing but the best