In kiosk mode, you can hide Home and Recents buttons.
It is not possible to hide or disable the Back button - Android OS doesn't allow that.
What you can do is to hide the status and navigation bars in the kiosk content application (use the "Full-Screen" or "Immersive" mode). This will still let the user to open semi-transparent bars by swiping up in the bottom of the screen. This action can be physically prevented by using special cases.
The default behavior of the "Back" button is closing the activity. Headwind MDM will restart the content app immediately. However, to prevent closing the content app, we recommend to intercept clicking the "Back" button in the content app.