FIRST Aid Kit are the Everly Sisters. Not since Don and Phil have two sibling voices entwined so divinely as those of Sweden’s Soderbergs, Klara and Johanna.

It has taken a while – their cover of Fleet Foxes’ Tiger Mountain Peasant Song was a YouTube favourite in 2008 – but their third album finds them signed to Columbia; the big league now.

Nevertheless, they have stuck with producer Mike Mogis, who worked wonders on 2012’s The Lion’s Roar, an album whose tribute to Emmylou Harris and Gram Parsons is impossibly beautiful.

Swedish they may be, but the Soderbergs look to America, sound American and Mogis and his sessions players surround the sisters in acoustic guitars, woodwind, strings and the greatest of all country instruments, lap steel.

In this folk-rock glow, Klara and Johanna’s sublime harmonies sing of things that are not so sweet. They are young folk, but sense change in the wind, the need to move on and yet show a reluctance to break from life now. Hence that album title Stay Gold, a wish more than a likely fulfilment, but being in their company right now is bliss.

Conor Oberst, the prolific Nebraskan songwriter of Bright Eyes roots, would agree. He has engaged the Soderbergs for back-up singing on no fewer than six songs on Upside Down Mountain, his most summer-scented album to date and one that harks back to the “Cosmic American Music” of country lost soul Gram Parsons.

Buoyed by the contentment of marriage, Oberst is writing in the tradition of the early Seventies’ songwriters, although it is not all happiness here. His ending could not be more downbeat : Common Knowledge is a story of a suicide. Not evrything can be turned around.