I think a genealogical relationship is different than the actual meaning of the word.

In-laws are "related" by marriage only. Your wife's sister is no more related to you than is her husband. They both are only "related" to you by marriage, hence they both would be in-laws. I don't think there can be differing opinions if the definition of the word states the relationship.

Per Merriam-Webster:
broth·er–in–law noun
1: the brother of one's spouse
2a : the husband of one's sister
b : the husband of one's spouse's sister <----------