Complex sentence: Joan's paternal grandparents were Thomas de Beauchamp, 11th Earl of Warwick and Katherine Mortimer, and her maternal grandparents were Richard Fitzalan, 11th Earl of Arundel and Elizabeth de Bohun.
Split into simpler sentences: Joan's paternal grandparents were Thomas de Beauchamp, 11th Earl of Warwick and Katherine Mortimer. Her maternal grandparents were Richard Fitzalan, 11th Earl of Arundel and Elizabeth de Bohun.