It's not even quite clear whether the brother helped his sister, pleasured her, or taught her. Either way, she should be grateful to him after a fuck like that. It's funny to see how he uses both his phallus and her toys to develop his sister's anal hole. It's bright and exciting, and you can see the details that are so valuable in a process like this. I wonder what he will turn her on with next time.
To tell you the truth, considering the age of the brother and sister, it is quite normal that the brother became aroused by the sight of the naked girl in front of him. Maybe what happened next is not part of the plans of normality, but tell me honestly, would you resist such a dark-haired beauty? That's what I mean.