A collection of four small portaits on ivory

A collection of four small portaits on ivory
Probably France, early 19th Century, one signed Doisteau, one Roi
Each of them oval-shaped and in floral and foliate golden metal frame topped by entwined ribbon, one frame rectangular and beaded, lined with green velvet border, three portraits depicting young ladies, one depicting Napoleon Bonaparte
7.5cm. (3in.), one 10cm. (4in.) high (4)