Definition: Your kids' in-laws (Merriam-Webster Online).
Sample usage: "The kinlaws are outside with their luggage and want to know if they can stay a week because technically we're family. Is that even them? It's been six years since the wedding."
Popularity: "Kin" isn't a word you hear up in this part of the country, unless people are also saying "kith" and the subject is: "words we don't use because 'relatives' is a perfectly good term."
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