You must have sex. A child cannot be made any other way.
Your father's brother is your uncle. His wife is your aunt.
The second wife to your father if she is not your mother is called your step mother .
Matthew is either the son or step-son of his father's wife.
A person's father-in-law is the father of their wife or husband.
He is your Father in law.
He would be the father-in-law.
He would be the father-in-law.
Father in law
A father's mother to the father's children is called the Grandmother (aka: Nana; Gran, etc.) The father's mother to his wife is the wife's mother in law.
A father's mother to the father's children is called the Grandmother (aka: Nana; Gran, etc.) The father's mother to his wife is the wife's mother in law.
If your brother-in-law is your spouse's brother, then his father is your father-in-law. If you brother-in-law is your sister's husband, then his father is not your father-in-law, and is not related to you in any way..
Your father-in-law is your spouse's father, i.e. your wife/husband's father.