Planning for interviewees

Im planning on interviewing my younger brother as he is a devout christian and is only 16 making him the best candidate for an interviewee, likewise his girlfriend is also a devout christian of the same age so she will be another interviewee. In fact both my brother and his girlfreind were the inspiration for this Idea, I noticed how sure they are of their faith at such a young age. I also plan to attend youth group with them this sunday and might come with surveys to make it easier or just go one on one with some of the kids there.