Good luck having positive results with 3S and using 12v regulators. As mentioned, they need a higher voltage going in than the desired output.
Under load, you will not be getting 12v. Do the math. Your 12v regulator will shut off or output lower voltage and your equipment will shut off. There is no point to this setup. Your intent is to filler the ripple. Do that. A filter and a regulator are completely different circuits, even if the regulator has a filter on it.