The easiest thing I can think is to use a signal repeater after your source, rather than using the TV apps. So for example, you would plug your cable box/streaming stick/whatever into an HDMI repeater which sends the same image to both displays, but only requires a single remote to control the source itself. That wouldn't solve volume, but that could be solved by using an external audio device.
For example: Source Device (media streamer, game console, cable box, disc player, etc.) > soundbar/receiver > HDMI repeater > TV 1 and TV 2
For example: Source Device (media streamer, game console, cable box, disc player, etc.) > soundbar/receiver > HDMI repeater > TV 1 and TV 2