I think Kotori telling Durbe was actually a smart move because lets face it: Yuma is an idiot and would probably never figure anything out. Durbe is the kind that would help plus since Shark is most likely Nasch its a major plot point for Durbe's development.
It will be interesting to see of the twins have to work for their Barian memories or if they just come back. And when they do figure out that they are Barians, do they go back to that side or fight against the other Barians?
As for the reaction, I'm not sure if Shark really understands that he's Barian yet and no one else knows yet.
Hopefully they keep Vector's character as the evil antagonist and don't change him to be good one bit. After what he did to Yuma its hard to see him as good in anyway whatsoever so suddenly making him good would be annoying like what they did with Faker. For once I just want an evil antagonist with no good whatsoever.