Your niece's daughter is your grand niece, or, as some would say, your great niece.
Your niece's daughter is your grand niece, or, as some would say, your great niece.
Grand niece.
You call them your nieces, or by their names.
Great-niece.
You would refer to them as your nieces, thought they are formally your wife's nieces. And they would normally call you uncle.
your 2nd niece...!
Your daughter and your niece's child are 1st cousins once removed.
My niece's daughter is my great niece.
Some would call your nephew's children your grand nephews and grand nieces, others would call then your great nephews and great nieces.
They are 2nd cousins.
No he did not. I am one of his grand nieces. He had one daughter.
Nieces.