I would talk to him trying to convince him not to cheat more in the exams and help him to study more before important exams. Also, if he continues cheating he will change and he will be hypocritical and I wouldn't be his friend anymore.
First of all, I don't like going into people's issues. So if she thinks that she's doing well, she should know. But if she is thinking about beeing unfaithful, I will talk with her, because if she doesn't want to be in a relationship with that boy, it's better break down that relationship to avoid pity
First. I'd try to convince my brother to stop smoking, because it's really bad for the health. If I can't convince him, Ill buy him an electronic cigarrette which is better than common cogarrettes, but I will never buy him any type of drugs.