The Chieftains assemble a diverse cast for this Christmas special. “St. Stephen’s Day Murders” is a comic original, written by Elvis Costello and Paddy Moloney, depicting family holiday strife; the rest are traditional, but hardly predictable. Kate and Anna McGarrigle make “Il Est Né / Ca Berger” heavenly, Marianne Faithfull brings grit to the fiddle-strewn “I Saw Three Ships a Sailing” and Rickie Lee Jones is full of yearning on “O Holy Night”. Like the perfect Christmas, The Bells of Dublin is rich with bonhomie.