I would say that lil' Zachary was indeed the most difficult to speculate upon, as his face is young, and still, somewhat pudgy and amorphous.
After viewing several images, grimacing, and attempting to understand the proportions of the lil' monkey-boy's face, I concluded that his nose, jowels, and saggy eyes betrayed the lighting, and made consistancy among the images very elusive.
Out of this troublesome research, I have compiled these images, and have created this possible future appearence of Zachary Hanson.