Your child and your nephew are first cousins, so your grandchild and your nephew are first cousins once removed.
Your grandchild is your aunt's great great niece or great great nephew. Your aunt is your grandchild's great great aunt (or, as some would say, great grand aunt).
Great niece or nephew.
Your nephew's child is your great nephew or great niece depending upon sex.Your nephew's grandchild is your great great nephew or great great niece, depending on sex.
If you have a niece or nephew, it is their daughter.
Your brother's grandchild is your Great Nephew or Great Niece and you are their Great Aunt or Great Uncle.
A great great nephew is the great grandchild of your sister or your brother.
The English language has no relationship name for the wife of your great niece or great nephew.
Neice or nephew no dummy its nephew
The relationship sequence:Your nephew/niece is a child of your sibling and your son's first cousin.Your nephew/niece's son is your great nephew (or grand nephew) and your son's first cousin once removed.The grandchild of your nephew/niece (your great nephew's son) is your great great nephew and your son's first cousin twice removed.
The relationship sequence:Your nephew/niece is a child of your sibling and your son's first cousin.Your nephew/niece's son is your great nephew (or grand nephew) and your son's first cousin once removed.The grandchild of your nephew/niece (your great nephew's son) is your great great nephew and your son's first cousin twice removed.
Your sister's great grandchild is your great great niece or great great nephew.
Nephew
Grandchild