What is your dad's cousin's grandson to you?
The grandson of your father's first cousin is your second cousin, once removed.
The grandson of your fathers second cousin is your third cousin, once removed.
Your grandson and great grand son could be cousins,(first cousins once removed), they could be uncle and nephew, or they could be father and son. It depends on how they are related to your children. If your great grandson is the grandchild on one of your children and your grandson is the child of a different one of your children, they are first cousins, once removed. If your great grandson is the child of a…
Your uncle's cousins are also cousins of one of your parents, so the question is the same as "How are you related to your parent's cousin's grandson." You and your parent's first cousin's grandson are second cousins, once removed. Your and your parent's second cousin's grandson are third cousins, once removed. And so forth.
Your granddaughter and your first cousin's grandson are third cousins to each other. You find their common ancestor that is, your grand parents, and count the number of generations separating them, there are Brother and Sister then cousins, you and your cousin would be one (first cousins), your children and your cousins children are second cousins and their children are third cousins and so on.