Legal Question in Family Law in California

The fact that your sister inlaw's name is on the title will raise an implication that there is a community property interest in the car. You need to gather all the checks etc that were used to make the car payments, and the source of the down payment. You will need this to prove that there is no community property interest in the car. You could also ask the sister inlaw's husband to agree to a transfer of the car into your wife's name alone and agree that there is no community property interest.