I can not see it very well, but I think the earrings of Princess Margriet are the same as the centre stone of her broche, compare with the broche on her riband. So I think the earhangers were centrestones form another elements (the cross from the emerald collier, and a smaller broche) worn as earrings:
I can not see Princess Maria Carolina de Bourbon de Parme too clearly too but I think her earrings are the tear-drop emeralds from the diadem indeed:
They look like the earrings once worn by Princess Mabel of Orange-Nassau, for sure elements from the Emerald Parure:
Princess Maria Carolina has some nice personal jewels, also emeralds, so to see: