Your Dad's niece is your first cousin. Their child would be your first cousin once removed.
Your niece's son is your great nephew and you are his great aunt (if you are a woman) or great uncle (if you are a man).
Your niece's child is your great niece if she is a girl or your great nephew if he is a boy. You are his great aunt if you are female or his great uncle if you are male.
Your father's niece is your first cousin. Her daughter is your "first cousin, once removed".
Your father's aunt's daughter is your father's first cousin. Therefore, she is your first cousin, once removed.
great great aunt.
Great-niece.
your 2nd niece...!
second-cousin
Grand niece.
You are her great-great Aunt (or great grand Aunt, depending upon your preferred nomenclature). She is your great great niece.
Second Cousin
Nephews and nieces
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
Your daughter and your niece's child are 1st cousins once removed.
Your niece is the daughter of your sister. If you have more than one sister, you can have nieces who are also the nieces of your sister, since they are daughters of the other sister.
My niece's daughter is my great niece.