Well Felipe looks good at least.
I love Leo's dress. It's cute, modest, and appropriate for her age, but fancy for the event. It's a cocktail dress for a teenager.
Little Sofia dresses conservatively in general. I believe she does so by her own choice. She's at an awkward age and she may not be all that comfortable with being fashion forward or with her body. She's super tall for her age. I think that's why she slouches - to be a little shorter. That's certainly why she wears flats most of the time. It must be awkward to have a body of a mature adult when you're mentally much younger. People look at you and think you should be dressing and behaving a certain way, but you're still reserved and not quite there yet. Hence, I'll give Sofia a pass. Louise of Wessex was also an awkward dresser during her teen years. She was also tall for her age.
I like the style of Leti's dress. It reminds me of dresses from the 50's. Glamourous and feminine. I don't like that it's plain black satin. Too somber when you have that much heavy fabric. That much black requires a little more skin (e.g. a square neckline with narrow shoulder straps). It needs to be punched up and "lightened" with some glitter, lace, or sheer fabric. Even a glittery belt and a statement necklace would've improved the look.