Re: how to call questions like "it is true, isn't it" and "it is not true, is it?"
Actually, just answering "yes" or "no" to the utterance "It isn't true, is it?" is confusing. If you answer (for example) "Yes", you can expect the next question to be "Do you mean yes it is, or yes it isn't?"
The better answers would be: "Yes, it is" or "No, it isn't."