I thought i made it perfectly clear that the backstory of star wars was an illusion it never existed. Unless you count rejected prototype scripts as a backstory.
Rinzler in the Making of Star Wars gave a full account of what the journal of the whills actually was it had nothing to do with the young days or obi wan kenobi or anakin skywalker neither characters were even created yet.
Also Laurent B. who wrote the annotated screenplays was given access to all the scripts.
Unless Lucas has kept the prequel outline and sequel series outline from them i don't even think they were even written. The facts from many sources pretty much make a solid case that Lucas made things up as he went along. Though the Original Ideas Did exist in embryo in the first treatments and drafts for star wars.
Leia was never at first intended to be the sister, Vader was not Luke's father in the beginning vader was just some facist general and not even a fallen jedi or sith Knight.
Did he combine the concept of Kane Starkiller the dying father with prosthetic Limbs, The evil General Vader and the Valorum character. I believe that he did. I also believe Luke ended up having a sister because in one unrleased permutation of the story Luke was a female, and Luke also at one point had a brother deak starkiller. Yes in one draft Leia was the cousin, but starting out and what ended up in the a new hope movie Leia was the Love interest. Also in Splinter of the Mind's Eye she was not his sister.
The first angle they put in Empire that Fans guessed she may be his sister because Vader was his father and also could sense him through the force, happened when he was on cloud cities weathervane and asked her to hear him through the force.
I think Carrie Fisher said that was a happy coincidance because it could have just been womanly intuition.
I truly believe Lucas did not canonize Vader as the Father and Leia as the sister til return of the jedi. Vader all along could have just as easily been lying.
Of course it makes the drama stronger when the heroes father is the villain he has staked his life to bring down, and the heroic image of his father he idolized was made up by Obi Wan. I mean you saw the prequels the selfless Idealistic Young Man Of Anakin did not exist he was selfish asshole from episode II to III.
I known Lucas likes mythological tales and figures so Vader really is Anakin's shadow self. The Sith are taught to embrace passion and the Jedi are taught to remain calm and serene.
There is also the possibility Anakin was really Vader on the inside and just kept those bad emotions, hate lust and fears in check. In the novelization they refer to it as the dragon inside him like some caged pent up beast waiting to escape and lash out. If their is one word to desribe Anakin in the prequels it is Angst.
You cannot divorce the vader character from anakin as they are 2 sides of the same coin.
It is easier for Obi Wan to Believe Anakin died on Mustafar because the truth is painful to him. There is some truism in his point of view that when he betrayed the morals and codes the Jedi stood by and betrayed democracy he killed the good man he was. He did not betray the prophecy, the jedi just misread it. He did bring balance to the force through his son and daughter and by his final selfless act.