I'm sorry your sister was hit by a drunk driver. Not sure about the DUI - the aggravated counts may be that it his 2nd DUI and therefore it is an aggravated offense. You may want to contact the police department to find out the status. If it's left their hands, contact your D.A.
The man was charged with Aggravated DUI based upon the fatality and of course his previous DUI. He could receive probation or a prison sentence, depending on how the case develops and other factors. My condolences.
This answer is not legal advise. It is merely informative. In order for there to be an attorney-client relationship, a written agreement between the parties would be required.