So I heard this song and I knew what I had to do.

You bet your ass I'm making ponies for the brothers.  In this crossover world, I like to think that the countryhumans are alicorns while the humans are pegasi, unicorns, and earth ponies.  I also think that the particularly powerful countries would have the flowing manes that Celestia and Luna have, i.e. Eternals, full-time entities, and empires (though the former empires like UK and France would probably lose their flowing manes when they lost their empires).

I might make more besides the royal family, who knows, but Mandoria pony is definitely getting the voice in the song, who he's singing to I don't know, maybe in this universe he and Prussia are brothers *shrugs*