Hi cosplayfox. I think the greatest improvement would be in isolating the subject from the background. If they're sitting there, you can either ask them to move to another location (that you've already scouted), or move the camera around so that the background isn't so busy or conflicting that it distracts from the subject. I saw some trees and bushes in the background of the photos. If you have the cosplayer stand maybe 5 or 7 feet or so from them and you zoom in a bit and open up the aperture, it would help a lot in focusing on the talent. Hope that helps and good luck!
Anime California 2014
(Will be holding panel, "Posing for Cosplay Photos")