Another tricky 10/11 DS. Besides lots of attitude to me, he's constantly having a go at his younger sister (8). He's always resented her, though they are also sometimes great playmates, but now he's always having a go at her, saying snide things, trying to wind her up. She's pretty tough and fights back (and so gets into trouble too - result for him of course) but it gets her down being constantly criticised and undermined. We've always used sanctions, set boundaries etc and I always talk things through with him but it makes no difference.
He likes school and behaves well. We recently moved so we're a bit short of social life so thrown together more than I'd like. Basically, it's all very tense with lots of shouting from all of us. I'm feeling overwhelmed and not sure how to deal with it. Any suggestions?