In California, can I insure a car that has my mother-in-law’s name on the title

No, in the state of California that will not be an issue. You can add someone to the insurance of a vehicle they do not own or have stake in long as they are listed as a driver. Insurance companies allow people to be listed under the policy as a driver only. Meaning, the person can drive the car and be responsible but don’t initially have to own the car. You must have insurance before you get license as well. However, to get insurance, you must be listed under some vehicle. For this reason, you can just add your son to the insurance policy as a driver and keep the car title in your mother-in-law’s name. Also, by him being a teen they should understand that he/she don’t own a car yet. Of course, you would just have to tell the insurance company right away that they are a teen and just need coverage as a driver.