Niceville couple and their five children returning home from a family reunion in Saint Louis killed when their plane went down near Demopolis, Alabama.   A Niceville family was killed Sunday when their Cessna C421 lost an engine then crashed near the Demopolis Airport. Fred Teutenberg, his wife, Terresa and their five children died in the crash. The Tuetenberg’s were returning home from a weekend family reunion in St. Louis when the accident happened. In Niceville, where the family was well-known and loved, people are mourning. The Teutenberg's were active in their…