There is no difference between "grandniece" and great niece." Some people prefer to use "grand" but others prefer to use "great" when talking about the granddaughter of one of their siblings.
You are a great great aunt or great great uncle to your great great niece (or great grand niece).
No. A great grand child is the child of your grandchild. The child of your grand niece is your grand niece or grand nephew, depending on the child's sex.
Your grandniece is the granddaughter of your brother or sister, and the daughter of your niece or nephew. Your grandnephew is the grandson of your brother or sister, and the son of your niece or nephew.
A niece is the daughter of your brother or sister. A cousin is the son or daughter of your parent's sister or brother.
The son or daughter of one of your siblings children is your great niece or great nephew. In other words, the grandson or granddaughter of your brother or sister is your great niece or great nephew.
You are a great great aunt or great great uncle to your great great niece (or great grand niece).
You are your grandniece's greataunt or greatuncle. Your grandneice may call you her greataunt, or if close to you, may call you simply aunt (or uncle).
your 2nd niece...!
You are her grand uncle (or great aunt) and she is your grand niece.
She would be your Great/ Grand Niece. Seeing as you are her Great Aunt or Uncle.
No. A great grand child is the child of your grandchild. The child of your grand niece is your grand niece or grand nephew, depending on the child's sex.
Great niece's baby is your great-great niece or great-great nephew.The system works like this:Your niece's child is your great niece/nephewYour great niece's child is your great great niece/nephewYour great great niece's child is your great great great niece/nephewYour great great great niece's child is your great great great great niece/nephew...
Your granddaughter and your grandniece are second cousins or third cousins to each other
Your grandniece is the granddaughter of your brother or sister, and the daughter of your niece or nephew. Your grandnephew is the grandson of your brother or sister, and the son of your niece or nephew.
your 2nd niece...!
The plural of grand niece is grand nieces.
Your great aunt's son is your parent's first cousin and your first cousin, once removed.