When the Quebe Sisters from Texas take a stage, and the triple-threat fiddle champions start playing and singing in multi-part close harmony, audiences are usually transfixed, then blown away. It’s partly because the trio’s vocal and instrumental performances are authentic all-Americana, all the time, respectful of the artists that inspired them the most. And whether the Quebes (rhymes with “maybe”) are decked out in denims and boots or fashionably dressed to the nines in makeup, skirts and heels, the fresh-faced, clean-cut sisters, all in their 20s, look as good as they sound.