Your daughter's grandfather's brother's son is her mother's or father's first cousin and her first cousin, once removed.
No, your father's brother's son is your cousin. Unless, you have the same mother in which case you would be both cousins and siblings.
Your mother's cousin's son is your second cousin.
Your mother's son is you or your brother. Your mother's son's daughter is your daughter, or your niece. Your mother's son's daughter's mother is your wife, or your sister-in-law.
B is A's daughter. A is B's father.
Father
Matthew is either the son or step-son of his father's wife.
Your son and your mother's sister are in a "Great Nephew/Great Aunt" relationship.
She is the co-mother in law of you and your daughter's father in law is your co father in law. :-)
They are your biological parents.
The second wife to your father if she is not your mother is called your step mother .
Father and son