What counts as an in-law?

I know, dumb question. But I can’t seem to find an answer anywhere.
Specifically, I know that my husband’s sister is my sister-in-law, and her husband is my husband’s brother-in-law, but is my husband’s sister’s husband my brother-in-law too?

Yes he is.

To further push this thread:

How about my sister’s husband’s sister? As far as I can tell, there is no “in-law” relationship there.

To me, my in-laws are anyone that my spouse calls family.
That would be my social definition.
Is there a legal definition?

And what about my son’s wife’s mother? She’s not my mother-in-law. Saying sister-in-law implies some relation to a sibling, which she doesn’t have. My cross-law?

The concept of in-laws is a legal/social relationship. Mother/Father/Sister/Brother/Daughter/Son-laws have a traditionally recognized relationship/kinship next in importance after actual blood relationships in common law.

In spanish, the word used is consuegro/a.
As far as I know, we don’t have an english version of this relationship.