I can also imagine that some Gandhabba, if inclined to Dhamma, will seek out appropriate places for listening to Dhamma.
From my understanding, yes, there should be possessions possible. I watched some videos about a Christian exorcist, he reported about several “demons” even taking possession of a woman. I think they must coexist in some way with the original owner of the body/Gandhabba.
In my view, these phenomena are well explained with Gandhabba as well.
(In another forum discussion, we discussed the case of baby-bodys, whose “ownership” can change -one Gandhabb leaving and another entering/being pulled inside (and using the body for the rest of his life)This also is explained well.)