I can't remember who, but I think there's a fighter who lost to a father/son pair. Or maybe he beat a father/son pair?
Roberto Duran fought both Viruet brothers, Edwin and Adolpho. But he did not lose to them. He defeated them both and is reported to have threatened to defeat their father.
Jersey Joe Walcott defeated Phil Johnson and his son Harold Johnson, I believe. I think all kinds of people, including Harry Greb, lost to both Tommy and Mike Gibbons.
dwight muhammad qawi...beat michael spinks and lost to leon spinks... i know its not losing to both...but best from top of my head.. and..larry holmes had a win and 2 losses against the spinks too...