One way to convey Friday night’s San Antonio Symphony program would be to report its mixture of French and Russian music, but the better description would be about all the fun that happened. The concert was American, too, featuring a twin-sister piano duo from New York City performing one of the French pieces, Francis Poulenc’s Concerto for Two Pianos. Piano duets rank as among the most challenging in all of repertory, mainly for getting the timing together. Music Director Sebastian Lang-Lessing has joked that it happens best when both players have the same mother. That was proved Friday night for the audience of more than 1,000 at the Tobin Center for the Performing Arts. Michelle and Christina Naughton played the brisk concerto with an authority and stylish precision that only sisters can achieve. From the opening section’s introductory thick chords to the octave-jumping melodies that followed in the waltzes, the orchestra told Prokofiev’s Russian-style version of Cinderella with dramatic flair. The “midnight” section growled like a bear, building tension as the tick-tock of the clock approached the deadline. The happily-ever-after ending was truly inspired. This quite possibly was the orchestra’s best performance of the season so far.