I like the style of Leti's dress, but not the color and it screams an updo.
Leonor's dress is pretty, but I agree it looks a bit too old for her, the style makes her look big. Probably it would look better on Mom.
Agree both girls are taller and bigger than Leti, they can't wear Mom's clothes. I think Leo can wear Grandma Sofia's clothes (ex. Valentino gowns) in the future.
Leti's very pretty Cos dress from the Palacete Albéniz fotos will maybe fit Leonor as it is loose and has it seems elastication in the waist. I remember when I saw it that I thought Leonor and Leti had swapped dresses because again Leonor was dressing too old for her years.