sibling-in-law
A sibling-in-law is the spouse of one's sibling, or the sibling of one's spouse, or the person who is married to the sibling of one's spouse.More commonly a sibling-in-law is referred to as a brother-in-law for a male sibling-in-law, and a sister-in-law for a female one. Sibling-in-law also refers to the reciprocal relationship between a person's spouse and their sibling's spouse. In Indian English this can be referred to as a co-sibling (specifically a co-sister, for the wife of one's sibling-in-law, or co-brother, for the husband of one's sibling-in-law). Rarer usage of the term is seen in "casual conversation" with the term brother-in-law describing the relationship with one's brother-in-law's brother: William's brother Charles has a brother-in-law called James (James being Charles' brother-in-law here not by virtue of marrying his sister but by being a brother of Charles' wife) with James referring to William as being his brother-in-law.
spouse's sibling or sibling's spouse
affinity husband brother