Worried about therapist's methods

Unfortunately there is nothing you can really do. Did the therapist tell you him/her self that she was requesting the separation? If not, you don't know the dynamics of this interaction. It is quite possible that your brother went to the therapist and vented to him about his relationship with his parents and the therapist encouraged him to create healthy distance between himself and your parents. The message that then gets passed on to you is that the therapist is TELLING him to cut off communication. I honestly don't think that your brother is being manipulated. Is your brother older? Do you know how your brother interacts with your parents? I hate to say it, but quite often one child gets the brunt of the harshness from parents (abuse) while the other kids are completely oblivious to what's going on and think things are hunky dory. I encourage you to talk to your brother about the situation and not jump to the conclusion that he's being manipulated.