Complex sentence: Caroline went to the school in St. Germaine founded by Madame Jeanne Campan and was good friends with Hortense, Josephine's daughter and Caroline's brother Louis' wife.
Split into simpler sentences: Caroline went to the school in St. Germaine founded by Madame Jeanne Campan. She attended the school at the same time as Hortense, Josephine's daughter and Caroline's brother Louis' wife.