If you're writing non-fiction, write non-fiction for crying out loud! I have a friend who wrote a non-fiction book and used fictitious names for certain characters (those who might have taken offense -- and legal action -- because of their portrayal, and a "composite" character who was intended to represent several people). He explained his use of these fictitious names in the introduction. But I really think that unless you intend to misrepresent the truth about individuals, knowingly and with harmful intent, you should use their real names. As jobydog pointed out, if somebody wants to take action against you they could contend that their identities are so "thinly veiled" in your telling of the story that their true identities are easy to infer. I understand that invasion of privacy can only be claimed if the invasion is likely to cause harm, but I'm certainly not a lawyer. I say, don't worry about the HIGHLY unlikely possibility that someone might sue you -- that's the publisher's concern, not yours. If they want you to change the names, they'll tell you. And you'll most likely need to change some identifying references as well. Keep going down that road, and you'll find yourself in the fiction aisle.