Take and wash the rocks good and then soak them in a weak bleach solution with a couple drops of liquid soap for about an hour, then rinse and dry.
Branches and bark should be heated in the over to about 225 degrees for an hour and let cool. If you dampen them a little, the steam will help.
Small branches and bark can be put into the microwave for a minute or two if they are moistened first. The steam will do the work. Just let cool afterward.
Very rarely is there anything bad on the rocks or branches but it is better to be safe, plus you don't want newly hatched insects all over the house.