I'm inclined to go this route instead of trying to wire up the existing screens. I like the parking mode feature that records if the car is moved or hit. As well as the dash cam of course.


Campark R10 Backup Camera 10" Mirror Dash Cam Video Streaming Rear View Mirror Dual-Lens 1080P Camera with Travelapse, 24H's Parking Monitor

 

Only issue would be relocating the receiver built into the existing interior rear view mirror. It receives the wireless signals from your key fob. Not sure where it could be moved to that wouldn’t degrade performance.

 

Maybe not have a major impact. I will have to test. It would also be powered off when the keyfob is in contact.

 

In addition to what Bob states above, the mirror has built in sensor & switch for the rear/side mirror dimmer, you will need to take care of those as well. Why not just buy a dedicated dashcam & naviks/navtool? They cost more but seamlessly integrated into the car.
Also, that kind of monitor/mirror messes up my vision when I look at it (could be just me because I have astigmatism)