Your grandfather's brother is your great uncle.
Your great uncle's daughter is your parent's first cousin.
The son of your parent's first cousin is your second cousin.
In conversation, however, you address such people by their personal names, not by their relationship to you.
Grandson :)
Your grandson.
Your grandson.
Your grandson is the great-nephew of your brother.
your second nephew
Nephew...
cousin!
Your uncle's sons and daughters are your first cousins.
You wold call them your brothers sons. Hope this helps :)
Your nephew?
Great niece
That would be your Cousin.