Cal. Probate Code § 2105.5

(a) Except as provided in subdivision (b), where there is more than one guardian or conservator of the estate, one guardian or conservator is not liable for a breach of fiduciary duty committed by another guardian or conservator. (b) Where there is more than one guardian or conservator of the estate, one guardian or conservator is liable for a breach of fiduciary duty committed by another guardian or conservator of the same estate under any of the following circumstances: (1) Where the guardian or conservator participates in a breach of fiduciary duty committed by the other guardian or conservator. (2) Where the guardian or conservator improperly delegates the administration of the estate to the other guardian or conservator. (3) Where the guardian or conservator approves, knowingly acquiesces in, or conceals a breach of fiduciary duty committed by the other guardian or conservator. (4) Where the guardian or conservator negligently enables the other guardian or conservator to commit a breach of fiduciary duty. (5) Where the guardian or conservator knows or has information from which the guardian or conservator reasonably should have known of the breach of fiduciary duty by the other guardian or conservator and fails to take reasonable steps to compel the other guardian or conservator to redress the breach. (c) The liability of a guardian or conservator for a breach of fiduciary duty committed by another guardian or conservator that occurred before July 1, 1988, is governed by prior law and not by this section.