I've seen a lot of attempts to try and hide the fact that "Vader is Anakin Skywalker". For those who want to do that, I propose, instead of recutting Vader's birth in EpIII, cut it out fully (plus remove any mention of the name "Vader"). Why, you ask? It's simple logic. EpI - Darth Maul. EpII - Palps gets Dooku out of somewhere. EpIV - Palps gets Vader out of somewhere. EpV - Vader is actually Anakin. Not showing Vader at all in EpIII will make his appearance in EpIV less suspicious than showing his birth in EpIII. And what about Anakin, you may ask? Well, he lies burned all out near the river of lava, Palps leaning over what seems to be a dead body.
There is, however, a problem - with EpIV. It's three dialouges - between Luke and Obi-Wan, Vader and Tarkin and Obi-Wan and Vader. Now, regarding the Luke-Obi-Wan, after watching EpIII we'll all know that Obi-Wan's lying, regardless if we know that Anakin is Vader or if we don't (the difference is, that if we dont know Vader is Anakin, the audience may go like - booo! YOU killed him, you lying bastard! Which actually makes perfect sense, knowing that Prowse during EpV shoot said that Obi-Wan killed Luke's father...). But. Any mention that Obi-Wan was Vader's master will ruin the suspence. It's not like it's hard to put 2 plus 2 together.
So yeah. Simple, yet effective, recipe:
1. EpIII - cut out any mention of name Vader and the birth in his suit
2. EpIII - make it seem like Anakin died on Mustafar
3. EpIV - cut out any mention that Vader was Obi-Wan's pupil
4. EpIV - Obi-Wan's lying about Vader killing Anakin, but clearly doesn't want to tell Luke that Anakin turned to the Dark Side at one point in his life.
5. EpIII/IV - some additional cutting may be done to explain how Vader and Obi-Wan know eachother. Particullary in EpIII, if we don't show Tatooine, it may be implied that Vader tried to hunt down Jedi, including Obi-Wan, and that Obi-Wan sooner or later came to Tatooine.
I think that's the most efficient way to hide the fact that Vader is Luke's father. The recipe, though, doesn't cover the sister thing. Plus everything's still a pain in the ass.