Complex sentence: The commandant at the Yazoo trading post Fort St. Pierre, M. du Codére were visiting Fort Rosalie, with a Jesuit priest as they heard gunshots they turned around to return to their ship, but warriors caught up with them killing and scalping them.
Split into simpler sentences: The commandant at the Yazoo tribe's trading post Fort St. Pierre, M. du Codére, was visiting Fort Rosalie with a Jesuit priest when they heard gunshots. They turned around to return to their ship, but warriors caught up with them, killing and scalping them.