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.
auntie .
Your uncle is your child's great uncle and your grandchild's great great uncle. Your grandson is your uncles great great nephew.
I call them my uncles
Well that would depend on if you were the biological grandfather. If so then the grandchild is also your grandchild. If the child was born to a child of your ex-wife and not fathered by you then they are no relation to you and you would call them by their name.
Nieces.
Chachi
second cousin
Bob No bog
Your cousin in law
Your brother's great grandchild is your great great nephew (if a boy) or great great niece (if a girl). You are their great great aunt.