The two girls would be first cousins, once removed.Whether you are a first or second or third cousin has to do with how many generations are between you and your common ancestor (not inclusive)So you...
Your brother's daughter and your daughter are first cousins to each other.Your brother's daughter and your daughter's daughter (your granddaughter) are first cousins, once removed, to each other.
Your daughter's daughter is your grand daughter. Your nephew's daughter is the granddaughter of your sibling (your brother or sister) The grandchildren of siblings are second cousins.
Your sister's daughter and your daughter are first cousins to each other.Your sister's daughter's daughter (her granddaughter) is first cousin once removed to you daughter.Your granddaughter and your...