The system we got comes with two ceiling mounted screens, an in dash player that controls the system, two wireless headphone sets, and a remote control. Oooh, it also has aux input jacks for stuff like video games. Of course, at 18 months, it will be a while before the kids can use the system to its fullest potential, but it's nice to know those things are there when the time comes.
As far as I can tell - I haven't had much time to play with it yet - the screens can operate independently of each other. One can be playing a DVD while the other plays a video game or listens to the radio. It's a pretty cool setup. Makes me wish I wasn't the one driving everywhere! I'd love to be sitting in the back with my playstation saving the world from zombies or something while we drive the hour to Grandma's house!! Maybe I can convince the wife to drive....