Let's try to settle this thing once and for all, or at least for a while.
The CA DMV web site says: No passenger vehicle, pickup truck, or RV may tow more than one other vehicle without a Commercial Class A license, with endorsement.
Commercial Class A license ? Well you can get one if you are a CA resident if you pass a medical exam, a law test, and a driving test with the vehicle you would tow. I recommend a truckers' school to learn. Then you have to get an additional, double tow endorsement for the license. All that requires is a driving exam under double tow.
But I suspect, you ain't gonna do that. So you cannot double tow in CA.