Are there plans for the twins?
 

When the twins are split up, I assumed it was to protect them from Anakin (they don't know that Anakin is led to belive that Padme died before giving birth). So, do Obiwan and Yoda ultimately plan to have the twins restore the balance to the force? Or is this something that was decided on in ANH?

It's pretty clear that they are hiding them for their protection and that obi going with luke goes to show that they want to keep an eye on him and in time lead him to being one of their only hope in fixing things.

Yoda has a premonition that Anakin was "the one" in that he was "the one to rail Padme and impregnate her with two baby Jedis" -- so although they are split up for their protection, they do want them to restore balance.

BTW, short of Leia sending R2D2 down to Tatooine, how else could they have planned this? Was Yoda planning to train Leia?

I think what was happening was obiwan and yoda were waiting for the force to put the pieces together.