Thank Sundance and a happy coincidence for bringing Los Angeles-based band He’s My Brother She’s My Sister to central Europe’s hippest film festival.The foursome — formed a couple of years ago when brother and sister Robert and Rachel Kolar decided to start performing together, adding roommate and tap dancer Lauren Brown and, more recently, British-born actor Satya Bhabha along the way — wowed audiences at the Karlovy Vary film festival with their folksy mix of blues and jazz. The appearance came six months after fest executive director Krystof Mucha saw them play at Sundance — the band had driven nonstop for 12 hours from L.A. through snow and ice storms for the gig — and he immediately invited them to play the confab. Combining cello, guitar and a tap-dancing Lauren in lieu of a drummer, the band blends the styles of the 1930s, ’70s and East L.A.’s hipster zeitgeist. Playing nine gigs in the space of a week — many of them at the festival’s VIP central, the Grand Hotel Pupp — they swiftly made their mark. Robert, who also plays with Lemon Sun and has a role in Monte Hellman’s “Road to Nowhere” (scripted by Variety executive editor Steven Gaydos), explains that he had split up with a girlfriend “who had always been an arch-rival of my sister” and when he invited Rachel to write some lyrics for a song about it, “Wilted Rose” — with, according to Rachel some “humorously nasty lyrics” — was the result. The collaboration worked. When Rachel’s friend and partner in a theater company Lauren was asked to fill in for a drummer, the distinctive sound of the band was born. Satya, who moved to L.A. last year to pursue an acting career, brought his cello to the mix just in time for Sundance. The cinematic link does not end there — Robert and Rachel are grandchildren of late actor Robert Shaw. And proving there’s more to a film festival than just celluloid, Karlovy Vary topper Jiri Bartoska could be seen dancing the nights away to music from this filial group.