Whether live at a festival or bringing the party to your kitchen, Sister Sledge are gold standard Saturday night headliners.

He’s The Greatest Dancer, Lost In Music and Thinking Of You are aural euphorics: songs to bring hip-grooves and smiles to the even the inhibited and fed up.

All are from We Are Family, the Philadelphia sisters’ 1979 album named for the track which remains a staple of disco at its most popular and vital.

Debbie, Joni, Kim and Kathy Sledge had formed the group as young teenagers back in 1971, scoring a couple of modest hits such as 1974’s tempestuous Love, Don’t You Go Through No Changes On Me.

But with We Are Family, they went stratospheric, scaling heights they wouldn’t see again, despite delivering the odd hit – 1985’s Frankie was a UK number 1 – and a succession of respectable albums.

We Are Family’s album cover – a feature of many an 80s bedroom – shows the sisters in stylish robes, looking as refined and aloof as Chic on their 1978 classic C’est Chic. Two of the dapper

gents pictured on the latter, Chic leaders Nile Rodgers and Bernard Edwards wrote, arranged and produced We Are Family, still a compelling listen 40 years on.

Working with the duo was an inspired disruption, oldest sister Debbie remembers.

“We were all a little like: ‘What are we doing? This is so new!’” she says. “The way they worked was so different. They constantly worked together and they wrote as they went.”

Debbie adds: “It was a great synergy and very exciting. We had no idea where it would take us.”

Previously the sisters had chosen lead vocalists between themselves but for We Are Family, label execs called the shots.

“That was fine because we knew each one of us could handle it,” says Debbie. “It was right about the time of the great success of the Jackson family and I think they wanted to compare us. Kath was the youngest and she did an awesome job on lead vocals for We Are Family and Joni did an awesome job with Lost In Music.”

Both will be absent from Doune. Kathy, formerly estranged from the band, is touring herself this year, Joni passed away in March 2017. The rift was healed just weeks before Joni died at the age of 60 at her home in Arizona.

Kathy, who has lived in Phoenix since the late 1980s, says carrying on without Joni wasn’t easy.

“It was a devastating thing when Joni passed,” she says. “But we had to go on. One of the things we knew was important to Joni and important to us, was to give her her props and remember her. It gave us a chance to relate to the fans, our public family. They really did comfort us.”

Joni’s son Thaddeus Sledge will join the sisters for this exclusive Scottish festival date, as will Phoenix singer Tanya Tiet and Phoenix Afrobeat Orchestra frontwoman Camille Sledge – Kathy’s daughter.

“We’re very fortunate to have Tanya and Camille and Thaddeus Sledge,” says Kathy. “It’s a real family affair. It’s never a chore: even if the travelling part is a little wearing it fizzles out in comparison to the fun we’re having. We’re having a ball with these festival dates, they’re off the chain.”

She adds: “One of the great thing about these songs and the reason for their longevity is the fact they’re such happy songs.

“There’s so much joy in them and I think everyone can relate to that. We need that support from each other. We all need that belonging.”