Complex sentence: Marie's paternal grandparents were Robert VII, Count of Auvergne and Boulogne, and Marie of Flanders, and her maternal grandparents were Bernard I de Ventadour, Count of Ventadour and Marguerite de Beaumont-au-Maine.
Split into simpler sentences: Marie's paternal grandparents were Robert VII, Count of Auvergne and Boulogne, and Marie of Flanders. Her maternal grandparents were Bernard I de Ventadour, Count of Ventadour and Marguerite de Beaumont-au-Maine.