What are the laws in California regarding monitoring phone calls?

I recently found out my ex husband has been having his family (sister and probably mom and grandmother) listen in on our phone conversations about visitation and custody, even after I specifically told him not to. I feel these conversations are private and that the details discussed are between he and I as the parents of the children only, and adding in others just makes things complicated and messy. I've never said anything I regret and nothing mean or vicious or inflammatory or insulting, so it's not that I'm hiding anything. However, between my ex and his family they have managed to take most of what I say out of context and twist it to their own advantage, even to the point of adding information to make it blatant lies. I know what you're going to say, and I've since told him that all communication has to come from his lawyer in writing from now on (he claims he got legal counsel). I just want to know, if he tries to take what I said in twist it in court when I take him back in a few weeks, is there a law in CA that prohibits a third party (other than the police, etc.) from monitoring the conversation without the permission of both parties? Then his family won't be able to say anything without admitting they broke the law, and it will make my life so much easier.