I wouldn't really say much of that equates to anything. Either way, he's the #1 overall pick and whether he likes it or not, he's going to have a mountain of pressure on his shoulders. As scoutman said, this is the WHL now and his time for living a "normal life" is over. Whether you like it or not, that's the nature of sports now. The spotlight is bigger at a younger age, and if you want to make it, you have to be able to adapt.
From what I know, he's already a mature kid. If we're hypothetically playing these cards, I'm sure playing on a team with your older brother certainly isn't going to detract from your playing experience. Either way, the WHL doesn't look like it will make an exception so it will be a moot point.
I will agree, however, that he certainly should be playing Jr. A. Tons of players have played Tier Two as a 15 year old, and it's clear he's outgrown Midget hockey and has nothing to gain by going back to it.