Your Great Uncle's son would be your 2nd cousin.
Your uncle.
Your son will be a nephew to your brother, and will call him "Uncle".
You do you call your sons's son your "grandson" !
You would call the son of a lord, John, son of Lord So-and-So
I'd normally call him by his first name. And the son of your aunt is your first cousin.
His name.
Your sister's son will call you his uncle, if you are a man, or his aunt, if you are a woman.
your co son.
If your sister had a son, then he is your nephew.
You would call your daughter's son by his name ex: Hi Jack.
your great nephew
The son of your brother is your "nephew".
The son of your parents is your brother.