Answer 1

For the camera flash (and not the display) ... see the first answer "Here's a little torch app for a website" (possibly other answers)
https://stackoverflow.com/questions/37848494/is-it-possible-to-control-the-camera-light-on-a-phone-via-a-website

When I looked at this, I got the impression that turning on the camera flash was not widely supported, but it was just a feeling.

The purpose of this answer is to point in the general direction; I didn't dig far enough to know if it works.