Would you do it?

A bit of backstory: my mom had me at 16, she didn’t want me so my grandparents took me in and raised me. I’m 22 now, barely talk to her. I see her a few times a year although we live in the same town. Growing up she never used to visit me on my birthdays or anything like that and I never got to spend Christmas with her. A year after she had me she had another kid and she raised her. Now she has another 3 kids all with different men. I speak to my siblings just as rarely as I do with her. Last night she asked me through my grandma if I was doing anything and if not if I could look after my brother. He’s 15, I don’t get why the fuck he needs a babysitter at 15 but whatever. I said yes because I felt bad saying no to my grandma. So he spent the night at my house, doing my head in all night with being loud. He’s only left today at 5pm cause he slept all day and wouldn’t leave. My grandma just messaged me saying my mom asked if I wanted to look after him again on his birthday which is at the end of the month. Then she messaged me again saying my mom wants me to take him in every other Saturday. Would you do it? It’s pissing me off how all these years she acted and still acts as if I don’t exist and only reaches out when she needs something. Like take care of your own fucking kids, don’t pass them around like you did with me. I feel bad if I say no to my grandma and I feel like that’s why she asks me through my grandma instead of asking me herself. Would you do it if you were in my shoes?