Just watched ROTJ... and I know this is probably drastic, but honestly, I don't think their is really much reason to have Leia be Luke's sister at all.... may also make future edits of the prequel trilogy easier to justify her "remembering" Padme as well.

And also keeping in mind future edits of the Prequels... if it is indeed concealed that Anakin and Vader are one in the same, obviously the transformation scene would have never been seen. When Yoda confirms that Vader is Lukes father, perhaps have a Luke with a "force flashback" to the scene of Palpatine saving Anakin and transforming him, and verifying to luke the truth..