luke had a sister but it was not meant to be leia.
you can’t tell me leia was ever truly meant to be his sister when both ANH and ESB tease a romantic relationship.
Westermarck effect - Wikipedia
True in the initial draft. But go look at Leigh Brackett's earlier work. She was a big fan of Greek tragedies and a Mary Shelley fanatic (Frankenstein - Prometheus Unbound author), who before marrying Percy Bysshe, was almost forced to marry her cousin. She always put certain parallel aspects of Shelley's (sexual familial relationships) and her life (almost started a romantic relationship with her cousin she didn't know about before discovering the truth) in her work.
Hell, the "I've (Bradbury) been waiting for you, Obi-Wan (Brackett). We meet again at last. The circle is now complete. When I left you I was but the learner. Now, I am the master!" was a paraphrased quote from her and Ray Bradbury's (yes, that Ray Bradbury) falling out in mid 60s. He learned under her tutelage.
shyt, just change out Leia for Jocasta (sister instead of mother) and Darth Vader for Laius. The original trilogy is just a modern retelling of Oedipus Rex.