These dynamic performers uphold a breathtaking folk sound, graced by charming harmonies. When the two sisters come together in ecstatic and seamless “blood harmony,” it’s a sound that continues to haunt long after the songs are sung, leaving an electrical charge behind like a sparkling tracer in the air. Still equally distinctive as soloists, Lily’s warm, smoky alto is the counterpoint to Madeleine’s crystalline, bell-like soprano.