Hi Mary,
I wish I knew the answer to this problem!
Teambuilding? Something that gets them to be on the same team? Could backfire...Science Olympiad? take up new activity together, like golf, tennis, cooking, that gets them building a relationship not based on academics? I haven't really done this yet, and find DS12 will tease or bully DS9 when left together (e.g. kayaking recently). However, DS12 is very protective of DS9 when they've gone off to camp together (without grownups around).
For us, I've been just trying to keep them separate. Don't do homework in the same area. Sorry I can't give any more advice but will keep reading to see if others have the "cure". Good Luck!
