I don't know how useful this will be but I figured I might as well share. My sister (who is bipolar) and I (DID) had some odd interactions growing up. The most notable were our fights.

Somehow, don't ask me how, my sister figured out in grade school that I had weird triggers that she could use when we got into a fight (this was long before I was diagnosed). She would purposefully draw out my different personalities to lead the fight to where she wanted it to go. Now that I look back on it, I'm completely baffled by this dynamic.

Another odd interaction came about in high school. My sister was always able to tell when I was talking with the others. I shouldn't have had any tell tale signs since I was well used to hiding my discussions by this time and she never noticed when the others were talking amongst themselves (or just talking in general), but as soon as I started to respond to one of the others she would know. It weirded all of us out (and angered a few of us), especially when she decided to use it as a new toy.