Regarding whether 3rd Density and 4th Density entities can be in the same room at the same time. This indeed can and does occur. How is this possible? These entities in fact do not see each other, because the one in 4th Density has its molecular structure moving faster than the other. In all cases where aliens are contacting humans, there is some of this occurring, for instance, when space ships are in 4th Density in your atmosphere but are not seen by humans. When the alien entities wish to be seen, they move their space ships into 3rd Density, zip about, and then return to 4th Density to disappear. Another instance is where aliens are in 4th Density, whether in their space ships or in residences near Earth. When they wish to be visible to humans, they move into 3rd Density for the conference. Then, as soon as possible, as they wish for their comfort to be returned, they return to 4th Density.
Your planet is entirely 3rd Density now, but will move over the next century into 4th Density. However, there may be parts of the planet, for administrative reasons, that still function in 3rd Density spiritually. These areas would need to be physically quarantined, as in underground structures, for a partial 3rd Density spiritual planet to exist.
Those alien groups visiting the Earth are almost without exception from the 4th Density. Some higher density entities are here on Earth, but in doing so interact with humankind in the same manner as 4th Density entities, so the description we will be giving to you applies. We are not, in this discussion, referring to 4th, 5th, or 6th Density entities who have chosen to incarnate into human form in order to assist in the Transformation. These entities are in 3rd Density, however heavy this might feel to them. Those in 3rd Density, who have experienced existence in a higher density, have returned to a time in their past. They are used to higher frequencies, more motion and greater allowance for movement and thought. To return to a lower density is commensurate with a human going into the water, to assist dolphins, even though the pressure of the water would feel weighty upon one. Now, these visiting higher density entities, who are here to contact humans as The Call might be given, prefer not to be in the heavier 3rd Density anymore than necessary. They move into 3rd Density to be visible to humans, and then get the heck out. Thus, humans perceive them to be disappearing.