In ANH we see Obi-Wan able to a limited degree survive death by an act of self sacrifice. Yoda too surrenders to death. Palpatine and Vader opt to extend their lives unnaturally either through Force manipulation or technology. So by letting go of his fear of death in order to save his son Vader is granted the boon of redemption (by the rules of the narrative).
He kills the Emperor, not to defend himself but to defend someone else in certain knowledge that he would not survive.
He couldn't do this without Luke staying his own hand via compassion.
At no point is this planned (unless Yoda was really referring to Anakin as the other hope and he has been building up attachment to his father in total contravention to PT era Jedi codes).
Luke's intention seems to be to rescue his father or die trying.
Vaders intention is to bring Luke into his sphere of influence and kill and replace the Emperor.
The Emperor's intention is to get Luke to kill own Father and be so screwed up by the experience he would have to replace Vader once his friends and the rebels are seen to die.
Ben's intention is that Luke will weaken the Emperor by removing Vader and keep the Emperor busy enough to not notice the station exploding.
Yoda's intention is to get Luke to face his fear, see what Vader has become and not become it. I suspect he could see what would happen next but didn't want to jinx it.
The PT versions of these characters only partially follow this pattern.
PT Yoda has written Anakin off from the moment he met him.
PT Obi-Wan spends the duration of his training of Anakin constantly putting him down or not defending him during every carefully staged moment of humiliation.
PT Sidpatine really has the hots for Anakin.
PT Anidar Doesn't accept refusal or rejection, Loves killing kids and wants to kill all his bosses.
The PT is very weirdly drawn and should have been directed by David Lynch.
