And for next year, your goal is to keep your current 6th graders from becoming culturally affected by the older kids that belonged to the old director. This means isolating them from the upper classmen as much as you can. If your standards are truly night and day different from your predecessor then this will likely mean your current 6th graders will eventually pass up your current 7th graders anyway,meaning you might have a varsity that's made up almost entirely of "your" kids. In that situation, "your"kids will be the majority while the handful of upperclassmen who made the cut will just the the whiners that nobody likes.
If there's still a bunch of 8th graders in the varsity next year you might want to try splitting it up so that all of Your kids are in a "7th grade band" together while the previous director's 8th grade kids are in a class together. And then switching it back 2 years from now when your current 6th graders enter 8th grade and the entire program belongs to you.