Frustrated, so sorry you are going through this. Sounds familiar! You've gotten some good ideas here already.
I am SO glad that our easy child is the oldest... difficult child looks up to her, as you said your younger kids do with-your difficult child. That is really hard. You'll have to spend time with-ea of them, alone, and make sure they have positive role models.
I looked up to my sisters, but they were pretty wild, too, and I never did the things they did because I didn't want the punishment. So you never know... they may catch on.
by the way, we rarely ground any more. It wasn't working well. We found other triggers. I'd suggest watching your difficult child closely to see what he values... football cards, computer time, etc. and take those away instead. Plus, grounding keeps him underfoot and then he drives you crazy. YOU aren't the one being punished, right? :wink: