Great post, and never really thought of it that way, cause I never think of 1-6 order, always thinking 4-6, 1-3. But I will even go a step further, and not even have Luke & Leia being named in ROTS either. And not even showing them going to their foster parents either so the only thing you see is Padme giving birth, having two kids and dying.
Thus the reveal in ESB is preserved about Vader being Lukes father, and the reveal about Luke/Leia being siblings in ROTJ is preserved.
Oh, I agree with you. Luke and Leia should not have been seen or named. In a world of good storytelling, Anakin's wife would have fled Anakin, probably with Obi-wan as her guardian, to protect her unborn child from what her husband has become (because the turn to the dark side wouldn't happen in five minutes), and the birth of the twins would happen off-screen, or better yet, between movies. The children and their fates would be unknown to the viewer until ANH. THEN, after her children have been safely hidden, she would try to confront (if at all) Anakin to win him over to the dark side, yada, yada, yada. So many wasted opportunities to weave a really deep and continuous story as opposed to a movie version of star wars theme ride.