Your grandmother's sister is your great aunt, her grand children are your second cousins twice removed.
Genetically speaking this is barely a relationship - but if you were raised together as cousins the familiar bond can be tight.
YesThe son and his sister = 1 son, 1 sisterThe sons and their sister = many sons, 1 sisterThe son and his sisters = 1 son, many sistersThe sons and their sisters = many sons, many sistersThough in reality this is a strange way to say it. More normal would be "The sons and daughters".
no problem man! enjoy
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
Your sister's son is her grandson and your great nephew. Some use the term "grand nephew."
My sister's son is my nephew.
cousin
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
First cousin, once removed.
If you have no siblings but your daughter has an uncle, he is the brother of your spouse, your brother-in-law.
Your granddaughter and your sister's grandson are second cousins.
They are second cousins
You are each others cousins.