Well, at least I know how to tap dance

I'm in a quandry. One of DH's brothers has had a life of health problems. While I don't wish any of his struggles on anyone, even someone I really can't stand, I also don't think he's provides a very good model for dealing with adversity. He's whiny, and because of his health problems he doesn't hold a job (even though I know plenty of people with the same struggles who are very productive members of society.) He mostly leeches off of his parents and complains about how hard his life has been. Somehow he has convinced a good friend of his from college to help him write a book about his life, about how sports and humor have seen him through his difficult times. He sent me a questionnaire for use in developing the book. Some of the questions are things like "What is your first thought when you hear the name [BIL]?" and "What has it meant to know me?" and "A funny story you can remember about me and/or your thoughts on how I use humor in how I deal with my medical situation." He asks how his experiences and knowing him has changed my views on the medical condition he suffers from. When he sent me the survey, I put it aside, trying to decide whether to respond. I don't have a lot to say that would make a difference in the book. His experience hasn't changed me, because my feelings on the topic have been the same for most of my life. I know other people who have the same issues he does, so his situation was not a revelation to me, it didn't expose me to anything I wasn't already thinking about. Some of his friends from the charity events involved with his condition are much more inspirational than he is (most of them are, actually.) So, I did nothing. Last night at dinner he asked me again about the survey, whether I had gotten a chance to fill it out yet. I said I had not, and told him that I didn't think I had much to contribute. I advised him to go ahead without my input. He insisted that he wanted to get everyone's response before going to the next phase of the writing, which is interviewing the closer family members (DH, MIL, FIL, etc.) So. Do I try to make up vague answers that will maintain family harmony or do I tell him that I don't feel comfortable answering the questions because I don't think they will be all that flattering? I don't want to end up being quoted or have views that aren't really mine represented in this book. I also don't want to go on record as being the cold and heartless beeyotch who would refuse to support her BIL. What to do, what to say?