Complex sentence: Blanche of France (1253-1323) was a daughter of Louis IX of France and Marguerite of Provence, and sister of Philip III of France and Isabella, Queen of Navarre.
Split into simpler sentences: Blanche of France (1253-1323) was a daughter of Louis IX of France and Marguerite of Provence. Among her siblings were Philip III of France and Isabella, Queen of Navarre.