-A retired Police officer hires two thieves to capture a cruel dacoit to take personal revenge

Foxtrot25, Think "Butch Cassidy and the Sundance kid" meet "The Magnificent Seven" (With singing and dancing)"

Happy go lucky ex cons? They got caught and have served time, how happy can they be about that?

Two ?ex-cons, long removed from their life of crime, must help a sheriff defend his town from killers... (that want to do something for a reason.)

Let me try to re-write it from the point of view of the thieves:
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"When two happy-go-lucky ex-cons are hired by a respected retired police officer, they must protect his quaint town and their new found loves from a gang of ruthless killers."