You wrote:

"A therapist treating a compulsive liar has refused, despite the patients repeated requests they do so, to meet with other family members o hear their sides claiming it is a violation of professional ethics."

If you are not the patient, how do you know about the therapist's refusal?

I just want to suggest that sometimes people do not always tell the truth when they report what their therapist said. I am not even suggesting that the person is lying; it could very well be they report what they think the therapist said or meant. It sounds to me like the therapist does not want to do this and so the patient has two choices: either try whatever else the therapist is suggesting, or find another therapist who will have the kind of group meeting you are talking about.