Fourth Cousins, twice removed
Your great nephew and your granddaughter are second cousins to each other.
Yes, your grandfather's granddaughter could be your sister, making her son your nephew.
Your great great niece is the granddaughter of your niece or nephew. Your daughter and your niece or nephew are first cousins. Your daughter and your great great niece are first cousins, twice removed.
Grandniece
Your sister's grand daughter is your grand niece or great niece. You are her great aunt or great uncle.
An uncle's nephew and the uncle's child are first cousins to each other. The uncle's great granddaughter and the nephew are first cousins twice removed to each other.
yes
Your nephew's son is your great nephew.
Your nephew's granddaughter is your great great niece. Depending on whether you are male or female, you are that child's great great uncle or great great aunt.
Their cousin, because your child is your nephew`s cousin, so your grandson or granddaughter is also your nephew`s cousin.
Their cousin, because your child is your nephew`s cousin, so your grandson or granddaughter is also your nephew`s cousin.
It depends - he could be either her son or her nephew.