No, cousins are the children of siblings. The children of my mom’s sister(my aunt) are my cousins. Grandchildren of my grandfathers brother(my great uncle) are my second cousins(as stated above). Of course here in the South usually any degree of cousin is just called cousin.
They are- and by definition they share at least one grandparent with you. Because if your mom and her sister didn’t have at least one parent in common, they wouldn’t be sisters.