You are close. @Quetzalcodename was showing you the nodes, not necessarily all connected. This is what you need to do, with an explanation after
The nodes need to be executed, so on construction of the widget, get a list of all cameras and store that. When you click on your button, you can then get one of your cameras from the list (I used 4 as an example) and change the view to that.
Now getting the actors will not always store them in the same order, so you probably want to get some more detail from your camera - eg a name - and then compare you cameras name to that of the camera stored in you array. This way you can be sure that the right camera is selected
Something like this:
We loop through each element of the array and see which camera name matches the camera name that we want, when we get a match, we then send that camera to be viewed.
If you do that for each of your buttons, where you simply change the camera name, then it should work for you.