$RootClass = new CLassRoot;
$RootClass->OneClass->MyFunction();
$RootClass->TwoClass->MyFunction();

class CLassRoot{
   public OneClass;
   public TwoClass;

   public function __construct(){
       $this->OneClass = new OneClass;
       $this->TwoClass = new TwoClass;
   }
}

class OneClass{
   public function MyFunction(){
      return 'Hello, '.__CLASS__;
   }
}

class TwoClass{
   public function MyFunction(){
      return 'Hello, '.__CLASS__;
   }
}