Complex sentence: He married, firstly, Lady Sarah Boyle, daughter of Richard Boyle, 1st Earl of Cork and Catherine Fenton and secondly, Elizabeth Altham, daughter of Sir James Altham and his second wife, Mary Stapers.
Split into simpler sentences: He married, firstly, Lady Sarah Boyle, daughter of Richard Boyle, 1st Earl of Cork and Catherine Fenton. Digby married secondly, Elizabeth Altham, daughter of Sir James Altham and his second wife, Mary Stapers.