a friend the kid you're babysitting nothing he's probably not even related to you maybe related to your mom as a third cousin but not with you plus you can't babysit him unless his mother gave birth to him at a really late time
your mom's dad is your grandfather and your grandfather brother is your grandfather too. so his wife will be your grandmaa and your grandma's sister will be your grandma too so, her son will be your uncle that's all
My grandma son is brother to my mom then he is called uncle how could be brother to me.