Help?!?

So I have my brother and his girlfriend baby sit often, there pregnant , young , no jobs and living with my mom. My sister told me there complaining I'm not giving them enough money for my 2 & 11 month old.

Baby sit time is about from 5 ish to 10ish

House destroyed by when I get home, with there mess too like soda cans or dishes

Kids are usually asleep by 7/8

I pick them up and drop them off back at home,

Also buy them dinner before taking them home

I typically give 40-60 and there wanting more. Thoughts? They also ask to babysit to get $