Complex sentence: Her paternal grandparents were Edmund Mortimer, 2nd Baron Mortimer and Margaret de Fiennes, and her maternal grandparents were Piers de Geneville, of Trim Castle and Ludlow, and Jeanne of Lusignan.
Split into simpler sentences: Her paternal grandparents were Edmund Mortimer, 2nd Baron Mortimer and Margaret de Fiennes. Her maternal grandparents were Piers de Geneville, of Trim Castle and Ludlow, and Jeanne of Lusignan.