Complex sentence: Stephen married Gisela, a daughter of Duke Henry the Wrangler of Bavariahimself a nephew of Otto I, Holy Roman Emperorand his wife, Gisela of Burgundy, a member of the Welf dynasty.
Split into simpler sentences: Stephen married Gisela, a daughter of Duke Henry the Wrangler of Bavaria, who was a nephew of Otto I, Holy Roman Emperor. Gisela's mother was Gisela of Burgundy, a member of the Welf dynasty.