I have had these types of surveys - and not just from the National Trust. My response to questions about my will, if I answer it at all, is 'None of your business'. It is, however, a sign of just how crass and patronising the National Trust is becoming
The National Trust is convinced that none of us can appreciate or enjoy any of their properties unless they have concocted one story to tell you about the house and no matter what your interest may be that story is all you are going to get. The story is frequently narrowly centred on one generation and, even, one person in hundred of years of history and their room marshalls are now trained to step forward and do their bit of carefully learned patter to everyone who comes into the room whether they want to hear it or not. Ask a question on anything else and they are completely ignorant.
Afterwards you get sent a questionnaire where one question is about whether you understood, or some such word, the story they wanted to tell you about the house. I get very tetchy about this. To reduce each property to such a narrow compass is an insult to the intelligence of their visitors, who come to their houses with a wide range of knowledge, experience and skills and whose interests go way beyond being told about nothing but the third lord and his eccentric family who lived in the house between 1900 - 1910.