I think Lucas confuses himself. I think he had something in mind with the Force back before 1977. But just because he had a father/son relationship, just because he had twins and siblings, and just because he was thinking of something biological behind the force does not mean that the solutions that appear in the films have any relation to his original ideas. They may have been born out of his original ideas, but it is obvious he pulled them out of his ass when he actually needed them. I believe that Vader was going to be someone’s father just from his name (a Germanic version of father), but we have no concrete idea who that was going to be. There are no clues in the drafts of the original screenplay. We have no idea who the other was that Yoda spoke of. And there is no way the idea of a symbiotic micro-organism had entered Lucas’s mind back then. And Lucas saying these things does not make them true. But I think there is a germ of truth in that when he went to write later installments, he was guided by his original thoughts and they led to the final storyline. I have lots of ideas as to what other possibilities might have resulted from the chain of events, but Lucas is remember ‘a father’ as ‘Luke’s father’, ‘the other’ as ‘Leia is Luke’s sister’ and ‘biological tie to the force’ as ‘midi-chlorians’. He had an early idea that he developed and the result really has no relation to the original idea.