We spent the weekend in Connecticut, guests at the home of my daughter's future parents-in-law. We hadn't met them before, but they were truly lovely people.
While we were there, I somehow brought up the topic of "what relationship are we to each other"? I'd been told that in other languages there was a word for it. So today my son came up with the Spanish word: consuegro, which translates as co-father-in-law.
Co-father-in-law turns out to be an English word,
albeit one I don't recall having ever heard.