On the left (standing with a striped skirt): Elsa von Dardel (83).
Standing in front of the windows: Georges von Dardel (64), Fritz von Dardel Jr. (62), Nils von Dardel (hat, 65), Carl Hederstierna (146), Louis-Alexandre de Dardel (7).
Sitting behind: Fritz von Dardel (20), his wife Augusta née Silfverskjöld (61), Gustav A. Boltenstern (1324), Lucie von Dardel née Palin (75), Augusta Ramel née von Dardel (19), Augusta Hederstierna née von Dardel (white hat, 66).
Newt row: Marthe von Dardel (dress with suspenders, 71), Cécile de Dardel née Perregaux (8), Augusta Hamilton née Lewenhaupt (5201 ?), Gustav von Dardel (light coloured hat & tie, 77), Marie von Dardel (2 ½ years, 78).
Lower row: Sophie von Dardel (white apron, 73), Fritz Boltenstern (3 ½ years, 5195), Nils von Dardel Jr. (the painter Nils Dardel at the age of 8, 85), Thure Boltenstern (5194), Fredrik von Dardel (84), Brita von Dardel (74), Georges von Dardel Jr. (boater, 76), Hans von Dardel (67), Amélie Boltenstern née von Dardel (68), Mathilda von Dardel née Norlin (69).
In spite of thorough researching, I could not find Augusta Hamilton née Lewenhaupt, but I think the lady on the picure is Amalia Lewenhaupt (1828-1902), wife of count Gustav Ludvig Hamilton (1817-1863) and daughter of Adolf Patrick* Lewenhaupt (1794-1871), sister-in law of Augusta Ramel née von Dardel (19 on the picture, herself sister of Fritz and Louis-Alexandre).
See also the description of the Montebello estate by Angela Rundquist.
See also the page on Fritz von Dardel the artist with a short biography and several pictures of his works.