You don't need variables in that case. Use the Success action of the button, choose Execute Advanced Action and with the Browse icon you'll get into the Advanced Actions dialog box.
This is an old video tutorial I once created, that shows how to use that dialog box: Video tutorial: Advanced conditional action for customized feedback
You only need a standard action, which is simpler, and you can use the Duplicate function to create one for each button, because there are three parameters that you'll have to change: Bt_one, Done_one and Slide_one.