ctrl-mvc-front-controller.php

This is the mother. Frontend controllers should extend this class. This class is a collection of required methods for all controllers and other commonly used controller methods.

No

ctrl-mvc-front-cross-site.php

This is the cross site controller that is always run alongside the controller for the template. It is accessed in the same way as the template controller via the $cross_ctrl global. JavaScript and stylesheets needed everywhere should be enqueued here

Yes