AITA because I don't take care of my sisters?

I (15f) have been taking care of my little sisters (10 & 4 years old) for as long I can remember. If they were hungry, I feed them, if they need help with work I helped them, if they were sick I took care of them, etc.. I've essentially been their mother. I never complained about it since I love them.

Now my mom doesn't see me as 1 of her daughters but as their nanny. It doesn't matter what I'm doing if they need something, she sends them to me. She yells at me if I don't make them dinner. She blames me if they misbehave, and she expects me to put my homework aside to help them do theirs. It's gotten to a point where I've failed assignments because I was busy watching my sisters.

Now I simply ignore my mom when she calls me to deal with them, which makes very upset to the point where she storms into my room and curses me out. I understand as an older sibling I have the responsiblity of taking care them it feels like too much of the parenting is on me. I don't want to think of my mom as a bad person but I have to put my priorities first, right? AITA

sidenote: I have 2 older siblings that can help as well