What is a therapist ethically allowed to share with the court in a family law matter?

Hi everyone! I come to you humbly as a family law attorney (sorry). I don’t make a habit of subpoenaing documentation/testimony from a therapist, but sometimes the court forces our hand & demands we arrange to have a therapist testify. I want to know - what can a therapist ethically share if their client is a PARENT in a custody matter? What can a therapist ethically share if their client is a CHILD in a custody matter? Are you bound by state ethical rules for this, office policy, both?

Obviously the scope of the case varies, but, for example, today, a hearing officer said he wants to talk to a child’s therapist about his mental health struggles he’s been experiencing in lieu of the child testifying. I am simply ignorant to what I can and cannot reasonably ask for (if anything) from a therapist - & I’m assuming he wants to know how the child’s parents factor into the child’s issues (alienation is a topic in the matter). Just an example. I am in PA if it’s state dependent but I would love to know anyone’s perspective generally! I don’t want to miff anyone off/ask for info/opinions I simply cannot have. TIA!