These are two legendary beauties of the day, Lily Elsie and Lady Diana Cooper, née Manners, daughter of Violet Lindsay Manners, Duchess of Rutland. Lady Diana became a noted actress and author, but I cannot find photos of her dating from before 1920 other than this one. Her article in thepeerage is here.
From wfpp.cdrs.columbia.edu/pioneer/ccp-lucy-duff-gordon/ via Pinterest search; enlarged one quarter and removed monocolor tint.
Neo-Directoire style dominates Lily Elsie’s dress while Lady Diana’s décolleté bodice adheres closely to her body. Diana’s train ends in a point, a Lucile trademark.
Keywords: 1918, Lucy Duff Gordon as designer, Lucy Duff Gordon, Lucile, Lucy Sutherland, Lady Duff Gordon, British
Lily Elsie, wavy coiffure, necklace, blouson over-bodice, vee décolletage, under-bodice, square neckline, quarter length sleeves, bracelets, waist band, draped over-skirt, train, tight skirt, shoes
Lady Diana Manners, Diana Cooper, Viscountess Norwich, Manners family, Cooper family, Viscountess, British, wavy coifure, necklace, under-bodice, elbow length tight sleeves, train, draped over-bodice, square décolletage, natural waistline, tight draped skirt, shoes