In the movie Sybil she had 16 personalities, before the psychiatrist had broken her down to realize this was a possibility her host personality was not cognizant of her alternate personalities. Some of her personalities however were aware of the fact that there were many more of them, for example one of her most dominant personalities Victoria spoke to the Dr. and revealed the fact that their were more. Were all of her personalities aware of each other existence?
Yes, they all knew each other. At the beginning, the movie shows a dark room where she introduces each personality while under the influence of another personality that was not Sybil. They also spoke to eachother. In this disorder, if they think they're someone else they'll see them in the mirror. When she's walking through the city talking to herself but in the mirror it shows 2 people, that's her recognizing the other personality.