Most of what you asked for is what I'd expect to buy off the shelf, but the moment you wanted integration with you in-dash unit it went far beyond the average user. You'll want it installed and sorted out for you.
I'd budget a few thousand for this.
I am not very "tech savy" so I was wondering if someone could help me figure out what to look for. We currently have an in dash after market touch screen "thingy" and it plays DVD's and our ipod hooks up to it and it also has USB hook up as well as AV in or out (I'm not sure). I would like to purchase dual portable dvd player that will play a movie on just the two screens (Ipod hookup would be nice, not sure if some do or not) but also will hook up to the in dash screen and play what is on the in dash screen. This way I have the option of the kids watching a movie on the two back screens and I can listen to music while driving still or have all three screens connected so a passenger could watch as well. I need help with the terminology because I read all the specs and I have no clue what anything means. Thanks so much!!