Marty Jr isn't an alter ego. Marty Jr is an actual character totally separate from Marty. I understand he is mistaken to be Marty Jr, but that doesn't classify it as an "alter ego" per say. He doesn't tell them to call him "Mary Jr" or actually ever go by Marty Jr. The question should be, what are Marty's 2 pseudonyms and leave out Marty Jr entirely. If we go by your logic then shouldn't there be four "alter egos" and include Darth Vader?