What to do?

I live at university 5 hours away from my parents. I have 11 yo brother and 3 yo sister. I have one grandma (dad's mom) and one grandpa (mom's dad). My parents have decided to go for a trip for a week, which means someone has to look after my siblings. My mom wants me to do it and I gladly would, but I have a bunch of classes that I would miss and 5 hours ride is quite exhausting, especially considering the day after coming back I'd have classes from 8 am to 8 pm. Grandma is very... Bad. She live 15 mins away from my parents but isn't good for children. She constantly yells at them, they have to eat what and when she says, have to watch what she says, wear what she says, there is no saying no in any way. My sister is already traumatised by her and my brother throws up for like 2 or 3 days after coming back from her. She was like that to me too so I know it's really bad. Grandpa lives 9 hours away and is sick so he can't look after them. Aunties also live far away so they aren't an option, so either me or grandma. I'd feel terrible to live them with grandma but at the same time I have my Chores to do and it's Hard to get back on track with one week of classes.