Complex sentence: Her paternal grandparents were Stefano Visconti, Lord of Milan, and Valentina Doria, and her maternal grandparents were Mastino II della Scala and Taddea da Carrara.
Split into simpler sentences: Her paternal grandparents were Stefano Visconti, Lord of Milan, and Valentina Doria. Her maternal grandparents were Mastino II della Scala and Taddea da Carrara.