In California motorhomes are specifically excluded from the 26,001 GVWR rule. The only requirement here is if your motorhome is over 40 feet than you have to have the non-commercial Class B.
You have to be real careful in how you read laws because they aren't always straight forward. I can show you a law in California that in fact does say you are required to have a non-commercial Class B for a vehicle with a GVWR over 26,000. So if you stop there you may think it is required. But there is a completely different law that exempts motorhomes.