My question involves name change laws in the State of: California

My Fiance has always planned to change his name to that of his "adopted" family (His name stayed the same as his biological mother, and the adoption was never completed due to biological parents interference ) What has prevented the name change currently is the nearly $500 price tag the courts want for a legal name change. I have never considered taking his current last name, and we both plan on taking his "adoptive" family's name. I know that in the state of California, both males and females are able to easily change their last name after marriage, but can we both do this at the same time? instead of me taking his name, can we both take a name neither of us currently possess?