My 2010 Town & Country didn't come with the dual DVD system. I just installed a MyGig RER radio unit. I want to add the dual screens in the overhead unit. I want to ask if all the wiring for the screens is already pre-installed in the roof for the entertainment system.

 

My 2010 T&C was not equipped with cabling to the overhead consoles. The cables came with the rear screen package. I ordered mine from a US dealer due to lower cost.
If you lookup the installation guide on the web you will find that instructions are provided as to how to install the cabling to the overhead console from the radio. I also installed the MyGIg RER radio.
Dave