Confidentiality is one of the most important elements of the sanctity of the relationship between psychotherapist and client. Successful therapy requires a high degree of trust with highly sensitive subject matter that, for many clients, is often not something they discuss anywhere but the therapist's office.
California law protects the relationship between a client and a psychotherapist, and information revealed by a client cannot be disclosed without written permission. Every therapist should provide a written copy of their confidential disclosure agreement, and you can expect that what you discuss in session will not be shared with anyone. This is called “Informed Consent." Sometimes, however, you may want your therapist to share information or give an update to someone on your healthcare team (physician, psychiatrist), your attorney, or other person in your life, but by law your therapist cannot release this information without obtaining your written permission.
It is not a therapist's obligation to investigate such suspicions but rather to report immediately to the appropriate authorities, including Child Protection/DCFS and law enforcement, based on information provided by the client or collateral sources. Preferably the client will be involved in making the report with the therapist so as to understand the process. Those authorities then make a preliminary investigation to determine whether there is an actionable concern. Note that therapists, by law, do not report suspected abuse such as domestic violence if it involves only independent (non-handicapped) adults between the ages of 18 to 65. Such domestic violence reports are under the mandate of medical personnel such as ER doctors attending to injured parties.
When the client threatens physical harm to another known person (e.g., homicide), the therapist is required by law to alert authorities (the police) as well as the intended victim. The goal is to maximize the safety of all concerned. In this case, if intent to harm affirms a threat of imminent danger, the client's confidentiality must be violated, again in the interest of protecting life and safety.
Generally speaking, all couples and family therapy sessions (meaning two or more clients in the room) are conducted with the understanding that information will be shared among clients without reservation, and clients themselves will commit to honoring the confidentiality of what their fellow clients reveal in session. With rare exception, therapists will not be obliged to keep secret information revealed by one client from a fellow client. The most important aspect of such situations, which may arise in therapy, is that the therapist will endeavor to assist clients to learn whether, when, and how to share difficult information with others in their lives, especially their fellow clients, and a key role of the therapist will be to facilitate such communication in session.