Personally, I think it's a case of semantics. I don't know how much memories are repressed as much as they are ignored. All the hysterical arguing over this issue seems to suggest that there's some magic being performed either by a survivor's mind or by a psychiatrist in reviving memories. To be it's really basic: When you are in a hopeless situation, it makes no sense to dwell on something that can't be fixed. So I think as a defense mechanism we simply push aside the memories and focus on more positive things. In my case, I can't say I ever lost the memory of what happened, but I certainly went for years ignoring it. And when it bubbles to my consciousness, the memories often come with greater detail. But that's usually because something triggered the memory that hadn't struck me before, so I'm remembering the event from a new perspective.
My advice to your boyfriend would be to allow himself to remember as much as he can without struggling to fill in the gaps, if there are any, or getting obsessed with remembering everything immediately. His memory will push out memories that he needs to recall.
As to the doubters in his family, I think we often want to deny unpleasant things. Just because who, after all, wants to deal with this mess especially 20 years later? Much easier to just stick your head in the sand and pretend it never happened. I have experienced this reaction from some people. The fact is, all of us fit into a network of friends, family and associates. Those people tend to like us the way we are. And anytime something emerges that's going to change the way we interact with them, we can expect resistance because we're disturbing their comfort level. Tell him not to sweat it. People who love him will stick with him and the people who only want him in their life for their own selfish convenient reasons will probably fall away. They may choose to stay in denial. That's their problem. It's upsetting in the beginning, but ultimately you learn a lot about who your real friends are.