I really have never understood the problem some have had with Leia and Luke being siblings. It’s not the greatest example of script writing in history, but it works and ties the plot together. It resolves the love triangle, explains why Leia was able to sense Luke with the force at the end of Empire and who the “other” Yoda was talking about was, gives Luke motivation to attack Vader (which is why any ROTJ fan edit would fall apart), allows for the existence of Kylo Ren (at least as Han and Leia’s son rather than Luke’s), etc. Even watching just the first movie, there’s nothing that contradicts it. Does it seem like kind of a crazy coincidence that they would happen to meet like that in such a large galaxy? Maybe (though not as much when you consider that they were connected via Obi-Wan), but the entire Star Wars plot is built on such coincidences. You have to suspend your disbelief a little and just allow “the force” to explain some of this to enjoy these movies. Star Wars is a fantasy with magic steeped in mythological storytelling tradition, remember, not some kind of hard sci-fi based on realism.