They'd make a heck of a walking stick topper too. (thinking the center one). Or the bottom half of the top one would be a cool knife handle...fill it with resin of some sort and put a crest on the "butt". Lots of possibilities there.

On working the stuff, I don't know if I can help you much on making buttons. But I have heard you really need a good dust mask when working horn...that's dangerous stuff to breath in.

Looking forward to seeing what you wind up with out of those.