Complex sentence: William Bonville jnr died along with his father at the Battle of Wakefield in 1460 and the castle fell to his newborn daughter Cecily, who later married Thomas Grey, 1st Marquess of Dorset.
Split into simpler sentences: William Bonville Jnr died along with his father at the Battle of Wakefield in 1460. So the castle fell to William's newborn daughter Cecily, who later married Thomas Grey, 1st Marquess of Dorset.