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.
The mother let her son do whatever he wanted, thus making his deepest desire come true, let him fuck himself in the ass.