If your pianos are plastic, rub them with a chamois cloth dipped in vinegar mixed with warm water. However, if they are ivory use a barely damp cloth and bit of gentle soap to wipe (remember – do not let the moisture leak down the sides); dry them ASAP. Use another damp cloth for the black keys. Buff with a third, lint-free cloth. Never scrub or use chemicals like rubbing alcohol. Take note: discolored keys like white turned yellow can be cleaned but could not be restored to their original whiteness.
You may be interested in the following related articles as well.
