@buoyantforce: Is this child of your Chair a not so stellar student ? Obviously, if the student was a strong performer, there would be little to worry about. But if he/she is not - and if the Chair has ambitious expectations for his child - then I can see why you anticipate problems. Getting a student to accept their limits is one thing. Getting the student's parents to accept it when they are both high achievers is another proposition.

If the situation is in the latter category the a discussion on ethics - however relevant it may be to the general situation bringing this all about - is no use to you. You need to discuss the matter completely frankly with a counsellor so you can better put your case to the Dean of Undergraduate Studies or whoever in university management.