If the ceiling plaster does contain asbestos and is in good shape, you are better off not doing anything to it. Problems happen when the plaster is removed incorrectly (dry, area not contained) and asbestos fibers become airborne. If your sample comes back positive for asbestos, you should have an industrial hygienist collect air samples (using aggressive techniques). Recommendations can then be made. If the remaining ceiling(s) need to be removed, have it done professionally by a licensed asbestos abatement contractor. You should get some recommendations from the industrial hygienist (if you used one).