No muffler, only cats, is that legal in CA?

The catalytic converter is the final component in the emission reduction system of any car. What you have done is actually made your car illegal for safety reasons because the exhaust must be vented away from the underside of the vehicle, ether past the rear bumper or out past the edge of the body. You could just put a pipe on the end of the cats and vent it properly and forget about the mufflers if the noise level is below state standards.