WheresBlackhawk said:

I've always thought that the most difficult thing about a NPT is the birth of the children. Creating a situation where one is born and hidden away, while the other is temporarily ignored, is really a difficult concept for me still. Any help would be appreciated there.

I agree with you here, which is why in the outline I hinted at above I would have Vader say something to NotPadme about Luke, this way we know that he is aware of the son, but when it turns out to be twins the daughter doesnt have to be hidden away, because we know that Vader didnt know about her, so she can just be passed off as Bail's adopted daughter without anyone needing to know who her real mother was.