Complex sentence: Henrietta Garnett, their second daughter, eventually married Burgo Partridge, her father's nephew by his first wife Ray; she oversees the legacies of both David Garnett and Duncan Grant.
Split into simpler sentences: Henrietta Garnett, their second daughter, eventually married Burgo Partridge, her father's nephew by his first wife Ray. She oversees the legacies of both David Garnett and Duncan Grant.