Complex sentence: He left the island at the age of ten years to return to France with his two brothers, Jean-Baptiste and Chériseuil, where he studied with the Oratoriens at their college in Rennes, and decided to enter their religious order.
Split into simpler sentences: He left the island at the age of ten years to return to France with his two brothers, Jean-Baptiste and Chériseuil. He studied with the Oratoriens at their college in Rennes, and decided to enter their religious order.