Complex sentence: He retired from Chatsworth when the Duke died in 1858 but carried on working at various projects such as the Thames Graving Dock, while Sarah remained at their house on the Chatsworth Estate until her death in 1871.
Split into simpler sentences: He retired from Chatsworth when the Duke died in 1858 but carried on working at various projects such as the Thames Graving Dock. His wife Sarah remained at their house on the Chatsworth Estate until her death in 1871.