Contact an experienced, wrongful death attorney in your locality. The attorney will investigate the facts and circumstances surrounding the death of your loved one, and he or she will make an intial determination as to who caused the death and what are the potential sources of recovery for the family.
You can sue him, get a judgement, then enforce the judgement. The process of seizing his vehicle is filled with pitfalls including the possibility that there are liens on the car. You might be better off contacting the Department of Motorvehicles and see what procedures they in place to suspend his license until he pays any judgement you received.