In what way could I control an android app from another app that could be on iOS or android?
My use case is I want to be able to control an android tablet that's part of a smart-home product. In this case I don't have direct access to the tablet's screen as it's encased inside the product. So I'd like to control the tablet via another android/ios app.
Specifically:
For part 1 I was thinking I could do something along the lines of have the tablet be in AP mode and use the client app to connect to it, is it possible to update the tablet's wifi once that is done?
If you were writing both pieces of software you could, although I wouldn't recommend it- Android is not meant to be a server OS, the battery optimizations and unreliability of Services make it a poor choice. Plain old Linux would be better. But controlling a 3rd party app remotely? You may be able to make something work, kind of. Something like connecting via wifi debugging, rooting the device, and sending raw touch events via the /dev/ filesystem. But it will be fragile, prone to breaking, and really hard to do. You're better off looking into open source solutions, like OpenHab.