you still call him DAD
He is your Father in law.
He would be the father-in-law.
He would be the father-in-law.
mother/father in law
You would call your wife's sister your sister-in-law. If your wife would have a brother he would be your brother-in-law. It is the same thing for a husband's siblings. Your wife's mother would be your mother-in-law. Her father would be father-in-law.
Your brother's wife is your sister-in-law.
A husband's stepfather is a step-father-in-law to your wife, but, if your wife is comfortable she can still call him dad and if not, she can call him by his first name.
The English language does not have a special term for the house in which a wife's father lives. You would call is, simply, my father-in-law's house.
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..
A person's father-in-law is the father of their wife or husband.
That's a relation by marriage. Your wife's father is your father-in-law.
Since your aunt is sister to your mother or father. Your aunt's dad is your mother or father's dad. You would call him your grandfather. Your aunt may also be the wife of your parent's brother. In that case, you are not related to her father.