Can I pair 2 apple TVs 4 th gen to 1 Apple TV Remote App ?

Sort of. You don't actually need to do anything the Apple TV remote app will operate both Apple TV 4's straight out of the box.

Yes.

The Apple TV Remote app should show all available TV's in your Wifi network for you to pair them. You can only select one to control at a time though.

With the new AppleTV remote app, it will have a list of them all you can choose when using the app. but to simultaneously control them (not sure if thats the direction you're heading) is not what it will do.