neice
Your brother's daughter is your niece..and you are her AUNT.
Great Niece.
Your sister's daughter is your niece and you are her aunt (if you are a woman) or her uncle (if you are a man).
YES
You are their aunt or aunt by marriage.
She is your cousin
First cousins twice removed.
That would be her great uncle I suppose. Common sense.
Your daughter's step-sister would be your step-daughter.
Your aunt's daughter is your first cousin.
Your younger brother's wife's sister's daughter would be your son's cousin.
Grandaughter.