Lady Sophia's article in thepeerage is here. Lady Charlotte can be seen here.
Upgrade image posted 19 December 2015 from Wikimedia.
The Fermor sisters wear similar dresses with full skirts, deep scoop necklines, and laced bodices in this portrait from about 1741.
Keywords: 1741, Seeman, Charlotte Finch - née Fermor, Sophia Fermor, Fermor family, Finch family, Carteret family, Countess, British, straight coiffure, floral cap, long straight coiffure, floral hat, scoop décolletage, laced bodice, jacket bodice, long tight sleeves, cuffs, elbow length close over-sleeves, cuffs, three quarter length close under-sleeves, cuffs, waist band, shallow vee waistline, peplum, full skirt