Legal Question in Real Estate Law in California

Which are you? Who actually owns the vehicle. If the grandmother bought the car and made all or most of the payments on the vehicle, even if she did not pay for the auto insurance, she would seem to be the real owner. But it depends upon what agreements she has with the granddaughter.

If there are two owners, one has no legal right to sell it without the consent of the other. You would be selling the other person's ownership interest without their approval. Nor is it wise from a family relationship view point to do such a thing.

You asked your question under the heading "real estate and real property," but automobiles are personal property, not real property. Therefore, your question got referred to LawGuru attorneys who specialize in real estate problems, not motor vehicles.

If the property were real estate, and two names were on title, here's what the law would be (and I think it's the same for personal property including automobiles, but I'm not 100% sure because there are some special provisions regarding ownership and titles in the Vehicle Code): Two names on title would make you co-owners, and if the title didn't say joint tenants, you'd be tenants in common and the co-ownership would be equal, 50-50.

Either co-owner could sell her half interest, but not the other co-owner's interest.

Since there is almost no market for half interests in automobiles, as a practical matter, no sale is going to take place without both co-owners participation.