the question is a hell of a vinaigrette.
What do you mean, "the $functions are redefined"?
$functions is a variable; there can be as many variables as you want.
Functions class? You use include_once, which means that the file with the class definition should only be loaded once.
Okay, you don't know a thing about programming, you're just taking your first steps in oo. Can you at least write the error in a human way? And give me code that corresponds to this error and does not contradict it?