Also, only the actual graphical display application uses Chromium/JS. The rest of the system is all C++. The display code has 100% test coverage, down to validation of graphical output (for example if you have a progress bar and you set it to X% the tests verify that it is actually drawn correctly).
As far as independent, completely independent from each other.
Indeed you can, judging by the instruction to power off and clean all displays (then power them back on) prior to ISS rendezvous/docking in the live stream.