I'm pretty sure that these guys predated the Beatles (even though their heyday continued well into the rock era). In fact, the future Beatles very likely heard a few Clancy Brothers tunes while they were still in Liverpool.

The Clancys were living in New York (or, at least, spending a lot of time there) in the early-to-mid-sixties, at which time they were acquainted with, and greatly influencing, the young Bob Dylan. Several of Bob's early songs featured his original lyrics sung to Irish and quasi-Irish tunes from the Brothers' repertoire (e.g., "Restless Farewell" and "With God On Our Side"). This was long before anyone in America ever heard of the Beatles, and *probably* before many Brits. The Beatles may have been famous in Hamburg by then, but I doubt that the Clancys were aware of them yet.