You said earlier that if you switch the positions of the buttons in the scene tree, only the first one works. Is that still true, using Debugging / Misc / Clicked Control?
You might try adding a third button, and see which of the three buttons' clicks is detected. You don't need to add code, just use Debugging / Misc / Clicked Control.
Also look at the controls in the 2D view, and ensure that it looks reasonable.