Body shareing is possible "also check out the spirit guardians thread for information of shareing your body with other personalities."
As with other spirits, it is possible. But most often its just other personalities and keeping with the three minds and three souls approach.
However sometimes other beings can "move in" to your body, although usually by kicking out something else. Or by squeezing in "basically its a nicer way of saying possessed "but possessed means becoming a possession to the spirit or other being that moved in. If it decides not to control you than its "sharing the space with you"
of course shareing would imply that it could take control from time to time but only when its necisary
Basically if the relationship is symbiotic you call it sharing,
if its parasitic than its a possession.
Also one must be carefull when departing on astral travels and leaving the body unguarded due to other spirits whom can make themselves at home while it is an empty vessel.