The palace was originally a photo, I wish I could draw like that!
I ran it through a few filters, the main one I think being ... argh! Poster Edges. If I recall, that lines sharp edges (of which there were a lot) and posterizes the rest, which made it easy to select and delete the extra colours. Once that was done, it was just a matter of doing the effect to match the rest. I did the same thing for the pelicans too.