How to make analog stick less sensitive & other questions

So I'm making a game that supports both a controller and mouse. Problem is that I can't seem to find any way to assign to both at the same time. Am I expected to change key assignment in-game with a script?

The second problem is the right stick which is used for looking around. While it works it's too sensitive. But that I mean that unless the stick is perfectly centered 100% there is always at least some minor movement which means the camera is never actually still. This gets annoying fast. How to fix?

 

Your input controls are going to depend on your type of game so I dont know what kinda of behaviour you need to be shared with the controller and the mouse, but heres some info that should help with your other questions

In Edit > Project Settings > Input
there's two entries for Horizontal and two entries for Vertical. The ones toward the bottom are for joystick input so you should be able to increase the deadzone and reduce the sensitivity for your controllers separately from your keyboard.