You and your uncle's child are first cousins to each other.
You and your uncle's grandchild are first cousins, once removed, to each other.
The grandchildren would be the parents, aunts and uncles, and first cousins once removed, of the great grandchildren.
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 uncle's grandchild would be your second cousin because his grown son or daughter would be your first cousin.
Your uncle is your child's great uncle and your grandchild's great great uncle. Your grandson is your uncles great great nephew.
Your uncles daughter would be your cousin.
Your grandchild and your niece are first cousins, once removed.
You are his grandchild.
You are not related to your uncles wife sister. However some may think an aunt
Your aunts and uncles are the sisters and brothers of your parents. So they are "blood related." But you also call the husband of your mother's sister your uncle, and he is not "blood related." So aunts and uncles are not always really related to you.
You and your uncle's great grandchild are first cousin, twice removed.
Your first cousin's grandchild is your first cousin, twice removed.
The grandchild of your great grandmother's sister is your second cousin, once removed.