There’s a moment right at the very beginning of any Twitty & Lynn show that affords country music fans the chance to look back in time. Just after the band has played the signature intro to “Louisiana Woman, Mississippi Man,” Tre Twitty and Tayla Lynn shoot each other a glance that summons the electrifying chemistry of their grandparents: Tre is the grandson of Conway Twitty, Tayla is the granddaughter of Loretta Lynn. Audiences can’t believe their eyes. From that moment, for the next 90 minutes, they’re in the presence of living country music history.