He specifically states that he knew the relationship between Luke, Vader\Annikin and the twins when he was originally writing Star Wars two years before it was released. However, The original screenplay is wildly different than the 1977 film and absolutely nothing like the next two films.
The first screenplay has Luke Skywalker as a 60-year-old general, Annikin Starkiller is 18 and living with his father, Leia is a 14-year-old princess and Vader is a general in the Empire, not some legendary masked\cloaked figure.
None of the story or relationships Lucas continually claims were always part of his Original Vision® are even remotely present or even possible.
That he can sit there and state all those lies with a straight face is insulting. That he thinks no one will challenge him or bother reading the original screenplays or 1977 interviews shows how colossal his ego really is.