Not sure how much you paid for these, but you might read some of Kim Taylor's bits on woods for weapons work. Generally, Ebony is considered a very bad choice for partner work, since it is often very expensive and some varieties are hard but brittle, when they go, they go big and they WILL go. Ebony bokken are usually saved for solo practice (although why anyone does solo practice with a bokken, I don't really know...).
There is a wood out there referred to as "tetsuboku" and while very nice feeling and quite dense, it's certainly not unbreakable, I've personally gone through two.
Woodworking for weapons