In situations where a pair of male siblings are both married to women, those two women may refer to each other as sisters-in-law. This is not as direct a relationship as the sister-in-law relationship between each of these men and their brother's wives, but it is the best way to describe such a relationship between siblings' spouses. Sibling-in-law is the gender-neutral term to describe the relationship between a married couple and both their brothers and sisters and those brothers' and sisters' husbands and wives.
The term brother-in-law, sister-in-law or sibling-in-law is most commonly used to refer to the brother or sister of one's husband or wife. However, when a spouse's sibling gets married, the same term is used to describe the relationship between the two spouses. This is the term that is used in the United States and in many other English-speaking cultures, but some cultural traditions may use different language to describe the wife of one's brother-in-law. If one's brother-in-law divorces his wife, that woman can be referred to as an ex-sister-in-law. However, in informal situations and contexts in which keeping things simple is desirable, it may be easiest for the various spouses of a group of siblings to simply refer to each other by their first names.