Your mother's niece is your first cousin. Your first cousin's daughter is your first cousin, once removed.
The niece of your niece is your great niece (or grand niece) because she is the daughter of your niece's sibling and thus the daughter of either your niece or your nephew.
The daughter of your niece is your great niece. (Some say grand niece).
Your uncle's niece is either your first cousin, your sister, or is not related to you at all.
Your first cousin
Your niece's daughter is your grand niece, or, as some would say, your great niece.
Grand niece.
cousin
You call them your nieces, or by their names.
my cousons sisters boyfriens dads nieces grandma's favorite sons dogwalkers mothers friends mum twice removed uncles daughter
your great aunt.
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.
Mothers sister is aunt and son is cousin so daughter wouldn't that be a niece
your 2nd niece...!
Your daughter and your niece's child are 1st cousins once removed.
Daughter hates mothers should she send mothers day card to daughter