How do psychotherapists charge?

I recently managed to convince my mom to see a psychotherapist to help her cope with the challenges of a debilitating motor disorder. The therapist currently charges $220/hour and has recommended a family counseling session as well. This would largely involve each family member venting and brainstorming ways to improve our interpersonal relationships. However, this 1.5 hr counseling session would cost $600. The $600 comprises a $330 charge for 1.5 hours of therapy for my mom and $90/family member. I find this to be very cost prohibitive and cannot understand the rationale behind the way I am being charged for the following reasons.

1. Each family member is being charged an additional $90/head for the session. Why are we being charged when we are not technically her patients?

2. Even if we assume this is a form of group therapy, why should my mom be charged the full price for this session as she would in an individual session? From my point of view, she is not getting the level of attention from the psychotherapist she would be getting if she were one-on-one with the therapist.

I find this way of charging to be extremely cost-prohibitive and and would like to know if this is typically how psychotherapists charge their clients? Moreover, all this is out of pocket. I look forward to some input from the community. Thank you.