[MyDuke]

Duke just turned 1 year old, his brother from another litter, same parents, just turned 4 years old. My best friend has Duke's brother.
We have tried to have the 2 of them together a few times and failed every single time.
We tried to meet outside so there's no territorial problems, it's either one will snap at another or both will just barks. We have to keep them apart.
Duke has played with other dogs (including yorkies) at parks, on the streets and get along with everyone well.
How can I get him to play with his brother? It would be great for the 2 of us to have our yorkies play with each other but can't seem to find a solution.

Any suggestions or anyone with similar experiences?