He should be happy, shouldn't he? They are coming tomorrow, aren't they? I'm right, aren't I? (Am't I? would be too hard to say !!!!) Shan't is less common. Some people never use shall and shan't, though they, of course, understand them. I use shall and shan't a lot. Shall I give you an example? An example would be: "I shall have to do it myself, shan't I?" (Probably said in annoyance when you realize nobody else will, help you) Or... "I shan't have to do it myself, shall I?" (probably you'll be worried in case you might have to do it yourself!) I suspect shall and shan't are more common in England than America. Any Americans out there who can confirm this???? Also, I would guess that upper class folk use shall and shan't more than working class people. But I'm guessing. As to question tags in general - it all depends on how you say these things. They range from 'statements' to 'real questions.' It really does depend how you say them, doesn't it?

He should be happy, shouldn't he? They are coming tomorrow, aren't they?

"He should be happy, shouldn't he?" and "They are coming tomorrow, aren't they?" are correct. "Shan't he?" is used in British English, but I never hear people say that in America. You would use "isn't it" in a sentence where the subject is "it." For example, "It is very cold today, isn't it?" is correct.