How would you describe a character with multiple personality disorder without confusing your readers?
A good way may be to just subtly hint towards it with their actions. As the golden rule goes, Show don't tell
From stories, I have read and movies about multiple personalities, there is one central dominant one and others are submissive and then can take over
the brain functions and actions. I also have read that each personality is distinctive and that when the other one is what I call in charge, there is no memory
from the other personaily.
You should also read "Sybil" Which writes about a woman with MPD.