Amazon kindle fires, a couple of headrest mounts and away you go. The fold down screens are very poor quality. A faff to install and expensive for what they are. A tablet each for the kids, and they can watch their own films without arguing. If you have Amazon prime you can download a lot of films for free onto to the tablets or fill up a few micro sd cards. I’ve had the flip down, and headrest monitors, but the best was the Kindle fire for £35