Lawyer may cost alot and take a longggg time....

If the car/title is under your name that means you have 100% rights to it...If he were trying to sell it he would need the title along with your information.....

Reporting it stolen may not be a bad idea but if the cops find it they may press charges on whoever has the car.

Basically just get with the grandma or the ex and threaten legal action if the car isn't returned.....You don't want to mess up your credit!