It used to be the "done thing" on Wattpad to create an idealised cast for your story. That said,  the below don't really form a cast. I don't have a suitable image for everyone, and the images are just individual pictures that work; I don't actually picture the characters as looking like these people in any other image but the ones below. Nonetheless, here are a few happy near-matches to my imagination for you to chew on.

Our intrepid heroine, Pascale:

Louise Jopling - Self Portrait, 1877

Her baby brother, Baudoin:

Photograph of Phillipe De Lacy, circa 1925

Miss Cartimandua Silverstar, vedette of the stage (and the embassy circuit!):

Photograph of Clara Bow. I'm not sure where I originally saved this from or when the photo was taken - if you can make out the date in the lower right, I'll add it!

The Allegedly-perfidious Archduke, Prince Ruprecht of the House of Elphberg:

George Dawe - Portrait of Leopold, Prince of Saxe-Coburg-Saalfield, no later than 1825 (but probably earlier, look at that fabulously Napoleonic uniform!)