This is how I have handled saplings - although I have never done so with hornbeam.
I seal the ends, split them and clamp them in a caul to help prevent warping. If you want to remove the bark you can just seal the back good. I would let them dry a few months at least before doing much with them. If you are in a big hurry, you could rough out a bow while it is green and it will dry faster.
If you don't have a caul available, you can split them and place a few spacers inbetween the two halves and clamp them back together (you can use duct tape if you want).
Mitch