In a traditional family structure, a father-in-law is the husband of one of the parent(s) of the family member who has married another family member. A common example would be a daughter marrying a son.
If the man who is the father of the father-in-law is also the father of the mother of the husband of the daughter, the man would be considered the mother’s father, and his wife would be considered the mother’s mother. This situation is similar to the one described above, except that it involves fathers and mothers rather than sons and daughters.
In the event that the father-in-law and mother-in-law are not related by blood but have been living together for several years, the man would be FAMILY LAW called the husband’s grandfather and the woman would be called his grandmother.
For men, there is no word in English to describe the position of a grandfather-in-law to someone else’s child.
If a woman has been married three times, she would refer to her previous husbands’ fathers as grandfather-in-laws, but never as father-in-law.
