Completely, literally tangential, but The Host by Stephanie Meyer (the author of Twilight) inadvertently has a very solid depiction of what it's like to multiply embody one flesh vessel; the point of view character is an alien brain parasite whose host body's original owner's mind is still present, and the two converse, fight, and find solace with one another, plus they have access to each other's memories but can also create barriers that prevent the other from intruding, etc, plus alien panic/desperate searching when the host seemingly disappears at one point. Very very true to my own experience being atypically dissociative and median, at least.

Again, obviously this is two years too late in terms of advice, but if I were aware somebody had been asking two years ago, this is what I would have pulled out.