The Movie is not a documentary, tho it looks like it is. It is an almost-behind-the-scene look at the 3 Brothers life on the road from concert to concert, and the things they care about. It's entertaining to watch but you will not learn anything new, not get any insights into the kids.
The 3-D is pretty good in that they don't over use the effect, but from time to time you realize it looks a lot better than on a flat experience.
Good singing, good performing, good clean goofing off among themselves.