L.R.
What a wonderful idea!!! You could have folks make tye dye T-shirts and bead necklaces and bracelets. That way you reinforce that we are family but each of us is special and have unique gifts.
Pre-Teen boys like games like Playstation and Gameboy but also card games like Yugioh and Pokemon and Munchkin. My 11 year old son loves to play most any game however. The books by Gary Paulson (Hatchet is the first) are great for boys. This age also likes to buy their own things so gift cards are nice. I bet he'd like cool sheets and towels of his own too. Maybe with monograms on them if that expense is affordable.
Good luck!