I am a twin but our scores were pretty different and we had different needs. So it wasn't hard for my parents to deal with each of our needs separately. (The fact that we were boy/girl twins may have also played a part.) When they talked to the school it was just about me because they didn't feel my brother needed anything different. Of course the fact that we were twins did play a big factor in the course of academic accommodations. If I had been a singleton I would have skipped a grade because that was what I wanted and that would have worked for me both academically and socially (all my friends were two years older). But that wouldn't have been good for my brother and so instead I was engaged with things like Olympics of the Mind and Science Fair and gifted classes and research projects and eventually honors and AP courses.
So I think the first question you need to answer is just how different are your kids' abilities and needs. If their needs are quite different I think you could just talk to the school about one of them. But if they both have very high abilities but different needs then I think you have to talk with the school about both of them, just for practical purposes if for nothing else.
As far as revealing scores to the school it is absolutely not necessary. But they can be incredibly helpful in convincing skeptical educators that you aren't just "that" parent and that you haven't just hothoused your children. It can be particularly helpful in that case to have both achievement and ability testing.
