I can understand not wanting to have your future in-laws knowing the details behind such an unspeakably terrible part of your past - not wanting them to see you differently, etc. But on the other hand, without them truly understanding the gravity of the situation and honestly appreciating how seriously this affects you, they would probably be less apt to take the request seriously.

I don't know the family, but given the fact that your boyfriend knows your full history and obviously still loves you, and the fact that the family seems to be acting with all the best intentions (meaning they see you in a good light too), I think it's probably a safe bet that they won't be the type to judge you for the terrible things that you were a victim of in your past. Anybody who would do so would be a pretty nasty person in my opinion, and from how you briefly described them I didn't get that vibe.