On my recent visit to my sisters place, we both wanted to teach our 3yo boys to share and figured with each other was a good start. At first I tried with Harrys lightning McQueens as he has 2.. This did NOT go down well with Harry, but Jubei didnt mind and even went and got his remote control Roary to try and make Harry feel better. It did work to an extent when Jei shared something after harry was forced to share. But it wasnt the answer.

What we wanted to get was something that was fun but NEEDS 2 people to work. Failing that we got them both a thomas train set and they set them up together and were playing happily together on their section. Unfortunately I had to come home and living over 10 hours away I can't go back randomly to keep it up, but I really felt like we had broken through there because not only wasy Jubei happy to play - but Harry actually set them both up together, then took Jei's Thomas train to him and ASKED him to come play on the set up with him.

I am not 100% sure what you can get that requires 2 people to make it work that is super fun that is suitible for an 9yo and 2yo, but I hope it gives you some ideas.