You might try boiling them but I think it might be too late.  Some people put bones in bleach to whiten them, the bleach destroys the bone.  You may be able to save them by soaking them in water and changing the water frequently and then boiling them.  
 
I highly recommend that you boil them for at least 15-20 minutes before you start work on them, then work outside.  The raw bone dust can have little critters that will live quite happily in your lungs, that can be fatal for you.

Bones can get flaky like that when they're old, sitting out in the weather too long. They may not only be old but structurally weak. If they're flaky and weak because they're old, boiling them may only produce soup. I don't know because I can't see what you're dealing with but flaking on bone is typically not good unless you want flakes.  
 
Maybe a light laquer, several coats then buffed with light sandpaper then steel wool to get a smooth and polished, but not glossy look to it when it's cured. It might pass; hard to say without seeing it. Laquer should fill in the minute cracks and spongy-like surfaces and strenghten the bone if that's what the problem is. Glue will work but elmers is not weather proof and will soften if in a humid environment or wet.  
 
If you were sent weak and old bone, I'd ask for my money back.