Are your btnYes and btnNo objects of "Button" type? In this case don't use Touch events for them. Use btnYes -> On clicked event instead.
If they are sprites, change events to Touch-> On touched object. "On touched" is a triggered event, it's triggered only once, which is what you normally want for menu buttons, toolbars, settings icons etc.
"Is touching" is a continuous event, it's executed many times per second, while the finger is touching the object. You should use it for controls like a virtual joystick, firing button etc.