relative-in-law

brother-in-law - a brother by marriage

daughter-in-law - the wife of your son

father-in-law - the father of your spouse

relative, relation - a person related by blood or marriage; "police are searching for relatives of the deceased"; "he has distant relations back in New Jersey"

mother-in-law - the mother of your spouse

sister-in-law - the sister of your spouse

son-in-law - the husband of your daughter