Your Great-Uncle is your father's uncle or your mother's uncle. Another way to look at it is to realize that your great uncle is the brother of one of your grandparents.
He would be your paternal great grandfather
not to be complicated , but if you have an uncle--> he has a nephew--> as you can see that's not complicated . And if you ask what is a uncles NEPHEW related to an uncles grandfather. in what way ....i would say the nephew is is the great gandfathers great grandson.
your uncles daughter would be your cousin
Your father's brother's son is your first cousin. Your father's brother's grandson is your first cousin, once removed.
Your aunt's great uncle's father is her great grandfather, or is not related to her at all if the great uncle married a sister of her grandfather).He would then be your great great grandfather - or not related to you at all.
Your grandfather's brother is your great uncle (some would say your grand uncle). You are his great niece (if you are a girl) or his great nephew (if you are a boy).
Your grandfather's sister is your great aunt.
Your grandfather's brothers would be the uncles of your parent. That would make them your great uncle.
Your grandfather's father is your great grandfather.
I believe they would be great aunts or great uncles.
It could be your grandfather. Or it would be a great uncle.
The brother of your great great grandfather is your great great grand uncle, or, as some would say, your great great great uncle.