I cannot find any information about either of them besides the title of this group portrait.
From pinterest.com/ccantiqs/18th-century-fashion-history/; enlarged one quarter. Also posted to the Reign of Louis XVI - 1775 to 1789 here.
Mme. Desroches dress is adorned with ruched sheer material at her bertha, engageantes, and the edges of her over-bodice and over-skirt.
Keywords: Madame Desroches Bournay, French, high large curl coiffure, hair jewelry, feathered ribboned cap, necklace, draped necklace, zone bodice, U-neckline, ruched bertha, bows, three quarter length close sleeves, forward-back flared engageantes, bracelets, full over-skirt, ruching