Sibling harmonies are so central to country that it’s remarkable that sisters Shelby Lynne and Allison Moorer have not sung together before, pursuing parallel glittering careers instead. Their voices interweave majestically on cover versions that stretch with surprising ease from bluegrass to grunge. Country stars such as the Louvin Brothers and Merle Haggard are an easy fit for the Alabama-born pair. Less expected is the gothic croon of Nick Cave’s Into My Arms, while the Killers’ My List and Nirvana’s Lithium are reframed from rock anthems to piano ballads. The one original, Is It Too Much, addresses the scars left by their father’s murder of their mother and subsequent suicide; a delicate, harrowing piece.