https://heleneltaylor.com/inheritance-separate-property/
The article itself is not important, the important thing is that there is CA constititution provision that is relevant to your situation. You have to show him the relevant law, such as CA consitution or CA statute.
So many know CA is community property state. It means any community property belongs to both spouse. However, there is also a separate property in CA marriage. Separate property is not community property and does not have to be divided in 1/2.
If you want to do this right, get a lawyer. You cannot DIY.