I'm still new to being aware of these parts being a possible reality. My experience is that there was one that just showed up out of the blue (whether he was there all along or not, I don't know) with what seemed to be the intention of sabotaging the relationship with our new T. The harassment started inside solely, with him trying to convince everyone that seeing this T was wrong. When I told the T about it, she made an invitation for this one to communicate with her, and I hate that she did that because it's not been good since.

Not sure if this helps, but that's my experience.