You granddaughter is a great great niece of your aunt. Your aunt is your granddaughter's great great aunt.
You are First Cousins
They would be first cousins once removed. Your great aunt's children are the first cousins of your parent.
Your son is a second cousin to your aunt's grandchildren. Your aunt's grandchildren are the children of your parent's cousins, making them second cousins to your son.
You would be your childrens second cousins uncle or aunt, i think... :)
Your aunt's son and her niece are first cousins to each other.
a nephew's kid to his aunt's kids would be their cousin.
Your son and your aunt's child are first cousins, so your son and your aunts grandson (the son of your aunt's child) are first cousins, once removed.
They would be first cousins.
3rd cousins
Your aunt's daughter is your first cousin, as is your aunt's son.
Aunt or uncle and they nephew and niece, there's not other relationship term that can fit that relationship unless in a mother tongue.
Your aunt's children are your first cousins and theirchildren are your first cousins, once removed.Your children and the children of your first cousins are second cousins to each other.