Legal Question in Wills and Trusts in California

Maybe, maybe not. If the amount the parents paid was equal to or more than the value of the vehicle, then it's over. There's no claim. This may easily be the case considering how much vehicles depreciate in value.

If they paid less than the value of the vehicle, then you have an arguable claim as at least a portion of the vehicle was community property if your husband (and/or you) were making loan payments after you got married. If this is the case, then you could seek to invalidate the transfer (or seek damages for the transfer) because it's a transfer of community property made without your consent (assuming you didn't consent).

However, what you really ought to do is to talk to your in-laws (and your own parents) about what your financial needs are in light of your husband's death. They may be willing to help out, but won't help at all if you seek compensation from them. Also, keep in mind that the loan payments made after you got married weren't likely all that much, limiting the amount of your claim.