App control another app I have a special scenario in which I should be able to update an app without getting any access to the phone. So I think of another app (something like a boot loader for the original app) which is installed side by side. So my question is whether an app can stop another app, update it, and start it back or is it completely out of question for a non-rooted phone?
If you are using consumer devices, one option is to use Android for Work or other Enterprise Mobile Management software which supports Android.

See: https://developers.google.com/android/work/requirements?api=clouddpx#35-silent-app-distribution

IT admins can silently distribute work apps on users' devices without any user interaction.

Or look at this StackOverflow post: PackageInstaller "Silent install and uninstall of apps by Device Owner” - Android M Preview which is off-topic for this group.