Names in the image title are from l. to r. in the image. Images of Princess Royal Anne can be seen here. According to her Wikipedia article, Princess Caroline died unmarried and childless. There are few images of her. Princess Amelia can be seen here. The Wikimedia caption is informative, "In this portrait the 26-year-old Prince is shown playing the cello with three of his younger sisters; from left to right, Anne, Princess Royal (age 24) at the harpsicord, Princess Caroline (age 20) plucking a mandora (a form of lute) and Princess Amelia (age 22) reading from Milton. In the background is the Dutch House or Kew Palace at Kew where Anne lived before her marriage in 1734 to Prince William of Orange. The suggestion of harmony between the siblings belies the antipathy felt by his family for Frederick; it is said that he was hardly on speaking terms with Anne in the year that this portrait was painted."