Tobar said:

The only reason they made Luke and Leia sister was to tie up the story into this one trilogy. Originally the "other" Yoda spoke about was supposed to be the star of episodes 7-9 but after ESB Lucas decided to just end it after ROTJ.

Not entirely true. At the time of ESB, Lucas did not have a clear idea on who "the other" was; originally - as we all should know - the twins were in the story right from the start and that idea went through various rewrites before he settled on the notion of them being apart from the start. That said, if he hadn't decided on Leia being "the other" in ESB, how do we explain her use of The Force towards the end of the film where she suddenly sense Luke is still alive and they should go back to him?

One of the ideas considered was that Han Solo was the other. I know you all like your little links on this forum - unfortunately I don't have one so, in the time honoured fashion that some of you have chosen, you can argue away 'til your heart's content :)