Complex sentence: He married twice: little is known of his first wife, his second being Alison St Lawrence, daughter of Nicholas St Lawrence, 4th Baron Howth, and widow of John Netterville.
Split into simpler sentences: He married twice: little is known of his first wife. His second wife was Alison St Lawrence, daughter of Nicholas St Lawrence, 4th Baron Howth, and widow of John Netterville.