The puppy formula that seems to work best is powdered (not liquid) Esbilac or Fox Valley 20/50. This is really all they need till they start to wean themselves off formula. Don't wean them off yourself, let them continue to take formula for as long as they want it. You can start making a quality rodent block available to them before they wean themselves. They will just shred it at first and make a big mess of crumbs but they will gradually start to eat more and more block and will stop taking formula when you offer it. Quality rodent block like Henrys, Mazuri, Teklad is CRITICAL to their overall health and development and to preventing MBD. Please avoid giving seeds, peanuts, lots of fruit etc, it seems counterintuitive but nuts are generally like fast food for a captive squirrel and will lead to MBD (it is different for outdoor squirrels which have access to a wide variety of naturally occurring foods). Here is a chart of what captive squirrels need after they transition over to solid foods:
https://thesquirrelboard.com/forums/...-Pet-Squirrels
Since you are in Ca, you probably don't have to worry about overwintering. We typically start the soft-release process at about 15-16 weeks old. This soft-release process is the method that gives your little ones the best chance of surviving out there. They don't have the advantage of a mom squirrel who can teach them what to eat, how to build a nest, escape predators etc, so just dropping off your babies in a nice, wooded area will be incredibly hard on them and they may well not survive. The soft-release process allows them to become gradually acclimated to outdoor temps, sounds and the general environment and trees nearby. If your location is not good or for some reason you can do a soft-release, it would be better to find a rehabber who can take then and provide a soft-release. Here is a link which details how to do a soft-release:
https://thesquirrelboard.com/forums/...-How-to-Sticky
Can you post up photos of your little ones? And please don't hesitate to ask questions! Good luck with your little ones.
Lastly for now, get a kitchen scale that measures in grams. Keep a daily or every other day log if what your squirrels weigh. They should be continuously gaining weight. A squirrel that is not gaining weight or worse, loosing weight, is a red flag that something is very wrong.