At my grandma’s rehab center, i’d see that the aids did all the work and the lpns told them what to do, and the rns passed out drugs. Is that the way it’s done?

Different work. There are multiple kinds of "work" in a rehab center or hospital. Some of this you never see, or may not recognize as "work". Making sure the medications are correctly prepared, documented, and given is work also. Different training, different responsibilities and tasks.