I plan to add activating via trigger press but this should be only possible for robots that have the button close (not sure if there's going to be an animation for that). But I also plan to turn other robots onto your side via an upgrade.
With sliders (UI) can you specify which part is problematic? BTW, if you have a cursor within a "slidable" part of a window, you may use a joystick to slide left/right, up/down.
I fixed recently a bunch of corridor related bugs (and also a few others, like enemies stuck in a room).
The engine is mine. Right now it is possible to create impossible spaces with Unity. It should be also possible with Unreal. Having own engine solves a few things that might be problematic with other engines - like spaces management, currently other games tend to have various zones on top of each other or next to each other which makes vistas a bit harder to do. But then, you get lots of tools that you don't have when you write your own engine. Unless of course you spend a while on creating those tools or you use Unreal/Unity or something else for that :)