Bleach would work, but I would be concerned about it retaining some inside the wood since its porous. If you do bleach them, make sure they are rinsed very well. Don't want any bleach still left in/on them. Bleach works great for tubs and other plastic items, though.
To be perfectly honestly, you really can't practically disinfect coconut hides. They will fall apart if you keep boiling them, and baking them might start a fire.
I recommend getting some simple plastic rock hides that can be scrubbed and disinfected properly with bleach solution. (Assuming aesthetics are important...if not, any upturned bowl with a hole cut in the side will do).