Your sister's son is her grandson and your great nephew. Some use the term "grand nephew."
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
Your sister's son is your nephew His sons are your grandnephews, and his daughters are your grandnieces.
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
cousin
Your son's children are your grandchildren.
My sister's son is my nephew.
cousin
Your grandfather's son's son could be:you (if you are a boy)your brotheryour first cousin
Your father's sister is your aunt and her son is your first cousin.
If you have no siblings but your daughter has an uncle, he is the brother of your spouse, your brother-in-law.
First cousin, once removed.