You and your great-great-great-great-grandfather's great-great-great nephew are fourth cousins, twice removed.
Your nephew's son is your great nephew.
The child of your nephew is your great nephew (if a son) or your great niece (if a daughter).
Your nephew's daughter's son is your great-great nephew. Your nephew's daughter is your great niece.
Your nephew.
Nephew
A nephew is a cousin to his aunt's son.
Your nephew and grand nephew may be parent and child. In not, then they are First Cousins, Once Removed.
brother
cousins.
niece/nephew
Cousin brother
nephew