In Robin’s defense, he said he heard stories about the Evil Queen but I don’t think he ever saw her in action, per say. Although, it would be shocking to find out next season if he did indeed witness Regina in full-on revenge mode.
Emma I don’t think is blind to what Hook did in order to get his vengeance. I mean, she was present for most of it. She knows the lengths that he went through but she sees now that he has changed and there’s a wonderful quote I saw on tumblr, that she sees he’s changed because she’s changed too.
In Belle’s case, I don’t know what to say about her. I mean, Hook told her point blank that Rumple murdered his wife and it didn’t make her flinch at all. And we also know that wasn’t a lie because we saw it. He grabbed her heart and crushed it. So, needless to say, it’ll be interesting to see how she reacts to finding out that Rumple murdered Zelena.