Replace rear audio system

If it were me, I would replace the entire system with an aftermarket system if you are having a problem with the factory one.

I attached a picture of a complete DVD system that is pretty cheap. However, if you want tablets, then just get two tablets with internet access and buy a couple holders that hang on the back of a seat and you can move them from car to car. At that point you can put any app or movie on it you want.

Technology today has completely changed the rear seat entertainment options to the point where you don't need any wiring or controls if you get the tablets. However, if you want just a DVD system, there are a ton of cheap options out there that will match what you want.