Elizabeth Ferrers British noble (1250–1300) Parents William de Ferrers, 5th Earl of Derby Margaret de Quincy, Countess of Derby Children John Marshal Siblings William Ferrers Robert de Ferrers, 6th Earl of Derby Joan de Ferrers Alianore de Ferrers Isabel Ferrers Agatha Ferrers Sibyl de Ferrers Agnes de Ferrers Maud Ferrers Joan de Ferrers Agnes Ferrers Partners William Marshal Dafydd ap Gruffudd