I asked, OK... but what about the spouse of your brother/sister?

and belM noted, The spouse of your brother is your sister-in-law, and the spouse of your sister is your brother-in-law.

I should have been clearer. I meant that it seems strange to me that both the brother of your spouse and the spouse of your brother are given the same title. I like how there is a name for the spouse of your spouse's sibling -- I have some very good relationships with my concuņo/as (plurals, consuelo?) -- and I was wondering if there was a difference between the names of the different relationships I mentioned above.