My wife’s father passed away and someone is driving the car with out permission (in Georgia) the car has gone missing on a few occasions

If you can't find the original Will, there may not be one. Assuming a reasonable attempt to find a Will has been made, someone should likely seek Letters of Administration as if there were no Will. That will let you get an administrator appointed for the estate. It may also let someone get appointed as a temporary administrator who can then legally get control over estate assets. As for the car, someone needs to get the keys locked up and away from the person who keeps taking it, if that's possible. It sounds like you know who it is. If you can't get the keys away from that person, then someone needs to have the car taken to a place that the person who has a key to it can't get to- like another person's locked garage. If you can't move the car, then you may want to try disabling it temporarily, so that it can't easily be driven- remove a wheel or two, take out the battery, etc, if that's possible. You are right to be concerned about someone driving the car without permission- if there is a crash that involves the car, there could be a lot of trouble, and the insurance company may not cover any damages.

You may never find a Will.  Two-thirds of Americans die without one.  Hire a local probate attorney to help you file an application to determine heirship and issue letters of administration.  As administrator you will have full authority over the deceased's property and can transfer title. Meanwhile, see whether a locksmith can change the door key to prevent hot wiring and joy rides.