AITA for refusing to babysit since I have to pay for my own room in their house?

I’m 17 years old, as my sister is 21 years old. I live in Australia but my parents are American, making it a lot more difficult to get into universities there. For that reason my parents arranged for me to stay with my aunts and uncles house in Arizona, and they will also be covering my school expenses. They said they would apply for a student visa for me. But they said I had to pay $600 a month for my own room in their house- which I’m happy to do cos it’s cheap compared to my friends who pay $800-1k to live in a house alone but have an extra day job to pay for it. This may be a side note, but I feel like it’s important lol. <br><br>So I stay in their house and I’ve lived there for 3 months now. I haven’t had any issues with my aunt and uncle. It’s my cousin that’s a problem. She has a 3 y.o son and she always comes over and leaves him here to play with his grandpa. But one day she had a shift and was overwhelmed because her boyfriend was at a mental health facility and she had to work late shifts. So she asked me to babysit for her boy. <br><br>I said no. That I’m a minor myself, and I’m in school, and I don’t know how to take care of a 3 year old child. But they began arguing with me, saying that I stay under their roof and pay rent, I am obligated to help them out. I said it isn’t fair, I’m already paying for my stay, I refused to be paid for babysitting and said that it is part of their responsibility. <br><br>My sister who lives here in Australia was also pissed with their attitude, saying they are taking advantage of me. But my other siblings (who live in America and are younger than 18) are on their side.