I wrote a memoir that's done rather decently, as memoirs go. I changed my JW family's names, as well as the names/identifying details of anyone else I either wasn't in contact with in order to get permission to use their real names, who was portrayed negatively, or whom I thought might wish to retain their privacy for whatever reason. I asked all of my friends who were portrayed in the book whether they would prefer for me to use their real name or an alias (all of them said that their real names were fine). This is standard when you write a memoir; actually, my publisher actively encouraged it.
Also, publishers these days can be really paranoid about memoirs due to the James Frey stigma...so they will likely put you through the wringer and require documentation of or witnesses to EVERYTHING you write, especially anything that might be considered controversial or seems wildly farfetched (as JW stuff, for example, can often seem). Lie-detector tests aren't offered as an option, haha. My publishers definitely put me through the wringer as far as verification goes. They and an attorney went through the entire book, page by page, with a fine-toothed comb and asked me to prove EVERYTHING. They called childhood friends of the family, former co-workers, former neighbors, they wanted my school records, paper documentation, emails, tweets...anything and everything that backed up what I wrote. It was exhausting, but I understand why it was necessary (yet still, to this day, I often get emails/Amazon reviews accusing me of making my story up because it seems too crazy. These people have no idea the lengths publishers go to these days to avoid a "Million Little Pieces"-type scenario.)
My family has never commented, but one person who believed that he was an anonymous acquaintance mentioned briefly on one page of the book, and didn't like the characterization, threatened to sue. However, my publishers basically laughed him off (I had already handed them mounds of proof for everything I wrote prior to publication, including the scoop on this guy), and not a single attorney would touch him, because I had changed the person's name and identifying details, so he had no recourse or claim, or even any proof that he was the person I was referring to.
So yes, definitely change names and also change identifying details (i.e., physical descriptions, workplaces/job titles) if the person is too easily recognizable even with the name change.