They provide more depth and creativity to a piece of writing.
I would tell them how their information would help enrich the research paper by providing detailed first-hand knowledge of a certain aspect of the topic and that if they can be quoted and use their name in the text of the paper it would lend a note of authenticity to the points being discussed.
What are your three main ideas? Also do you think they should or should not? I can write one for you you if you supply answers for my questions asked above.