Complex sentence: Her paternal grandparents were William Keith, 3rd Earl Marischal and Elizabeth Gordon, and her maternal grandparents were John Douglas, 2nd Earl of Morton and Janet Crichton.
Split into simpler sentences: Her paternal grandparents were William Keith, 3rd Earl Marischal and Elizabeth Gordon. Her maternal grandparents were John Douglas, 2nd Earl of Morton and Janet Crichton.