While I'm not against Leia remaining Luke's sister it doesn't really make sense that she is the 'other' spoken of in ESB.
Ben knows she exists, he knows she could be trained but in that scene only Yoda seems to have a clue who the 'other' is.
If possible I'd trim references to Luke saying things like "Yoda spoke of another" and Ben's "The other he spoke of was your twin sister" and replace them with a more general questioning about who this different Skywalker is.
That way Yoda comes across as more powerful because the 'other' he has in mind is Anakin (who does finally return and saves the day).
I hate it in film series when a later episode clearly refers to events in an earlier one as a film reviewer might.
Alien 3 has one of the worst examples of this, "When they first heard about this thing, it was crew expendable. The next time they sent in marines, they were expendable too. ... think they're gonna care about a bunch of lifers who found God at the ass-end of space?".
Luke's blatant reference to 'an other' is 'another' example of this (kids remember when Yoda mentioned a mysterious 'other' three years ago and you were really excited about who this new character was going to be? Well read on...).
It doesn't sound like what the character would say in that situation, it sounds more like a writer explaining the plot of his story to someone a bit slow on the up-take.
I haven't a clue how it could be done but at least by mentioning it the idea is out there.