Complex sentence: The Jonas Brothers appeared as musical guest on Saturday Night Lives 34th season on February 14,2009, making their "SNL" debut; this performance/appearance is the only time they have been on the show.
Split into simpler sentences: The Jonas Brothers appeared as musical guest on Saturday Night Lives 34th Season on February 14,2009, making their SNL debut. This performance/appearance is also the only time they have been on the show.