Complex sentence: Two of the most prominent California Impressionists who lived in Carmel and were known for their marine subjects were William Ritschel and Paul Dougherty, both of whom developed national reputations long before they moved west.
Split into simpler sentences: Two of the most prominent California Impressionists who lived in Carmel were William Ritschel and Paul Dougherty. Both known for their marine subjects, and had developed national reputations long before they moved west.