Movie plot holes

[Veho]

What's going on in that scene? Does Vader sense something familiar in Leia? He knows Luke is his son, did he ever figure out Padme was due twins? He was a Jedi, right? Wouldn't he sense both of them? Did Vader figure it all out before Return of the Jedi?

Taking the prequels into account, it's possible. But why would that stop him from killing (or letting Fett kill) Chewbacca? Maybe he was afraid Fett would kill Leia by accident, but that might be because she was an important hostage (one of the Rebellion leaders and a bait for Luke) and he needed her alive.

I don't think you can interpret the "look" Vader gives in that scene, because what with the lack of facial mimicry, he might as well be angry, sad, pensive, cunning, winking, smug, happy, scheming, thinking of puppies or any other expression you want to read into that immobile mask. The look Leia gives him does indicate she's as confused as you are: "why did he do that?"