Batman Family Values? It wasn't the megabucks or the cool costumes alone that persuaded Tommy Lee Jones to take the role of Harvey ''Two- Face'' Dent in Batman Forever. It was his 11-year-old son, Austin. ''[When] I went to meet with Tommy to do my spiel to get him to do the role,'' says director Joel Schumacher, ''I got there and Austin had a pile of Batman comics with Two-Face on top. Tommy told me he's doing the character because it's Austin's favorite.'' Father-son bonding aside, the character also fit the Oscar-winning actor's main criteria for a part. Says Jones: ''I like roles that are well-written, that are part of a good business deal, and that will take me to a pretty location.'' In this case, New York and L.A., beginning Sept. 21.