Your father's nephews and nieces are your first cousins.
Im not to sure, but I would have to say your Aunt.
Your grandfather's sister is your great aunt.
Most likely they would not be related to you
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
For clarity, lets call your great great grandfather's niece "the niece". The relationship sequence: (1) The niece is the daughter of your great great grandfather's sibling (2) The niece is a 1st cousin of one of your great grandparents (3) The niece is a 1st cousin once removed of one of your grandparents (4) The niece is a 1st cousin twice removed of one of your parents (5) The niece is your 1st cousin three times removed
Your great grandfather's sister is your great great aunt. You are her great great niece or great great nephew, depending on your sex.
The correct possessive form of "grandfathers" is "grandfathers'".
Your grandfathers' sisters' grandchildren are your second cousins.
Since it's her husband's niece the niece is just your sister's niece through marriage and not your niece.
Your sister's daughter is your niece. If you are a woman, you are your niece's aunt; if you are a man, you are your niece's uncle. Your sister's son is your nephew.
Your mother's niece is your first cousin. Your first cousin's daughter is your first cousin, once removed.
No. Your wife's niece is also your niece, but the husband of the niece is not related to you or to your wife.
Your niece's child is your great niece if she is a girl, or your great nephew if he is a boy.