Using Family Law Interrogatories
Interrogatories are highly useful, and have advantages for instance as compared with attempting to obtain information about the other party's case through deposition, because they can ask about legal contentions. That cannot occur at deposition because a layman cannot be compelled to give "expert" legal opinions about their case. In contrast, with interrogatories both the party and their attorney are deemed to be supplying the answers, and so the objection that a question calls for a "legal conclusion" is improper. Interrogatories cannot be used with non-party witnesses.
CALIFORNIA CODE OF CIVIL PROCEDURE
C.C.P. Section 2030.010
(a) Any party may obtain discovery within the scope delimited by Chapters 2 (commencing with Section 2017.010) and 3 (commencing with Section 2017.710), and subject to the restrictions set forth in Chapter 5 (commencing with Section 2019.010), by propounding to any other party to the action written interrogatories to be answered under oath.
(b) An interrogatory may relate to whether another party is making a certain contention, or to the facts, witnesses, and writings on which a contention is based. An interrogatory is not objectionable because an answer to it involves an opinion or contention that relates to fact or the application of law to fact, or would be based on information obtained or legal theories developed in anticipation of litigation or in preparation for trial.