Swap Object in GTK (using Python and Glade)

I'me trying to make a python app using GTK. What I want is to have a window with 3 buttons, and I want to switch the widget that is behind when I click one button (see screens for more infos). Also, if it's possible, I would like to make the buttons toggle buttons, but when I will click on another one, the previous will stay clicked. How to change that ? Thanks !

Screens :

I tryed loading another .glade file on another var, and use add1 on the panel to add it, but it didn't work (no error on the terminal).

Solution

It seems that using Notebook, as Alexander said, is the best way to do it. Thanks !