I don't know how much this will help, but when we moved next door to a boy my sons' age who has his own unusual social skills, there were some bumps. My sons were used to playing with each other and the other boy was used to playing alone. They wanted to play as a group but there were frustrations.
We very simply talked about 'practice'. It takes practice learning to play with different personalities, in groups of three rather than just two who have been playing together since they were babies.
The other thing we did was simply to keep an eye on the mood. Sunny outdoor-play days are when the boys are most compatible. They are least compatible after a library-visit, when my boys would like to read, or when someone is grumpy to begin with.
Most important, though, was explaining that 'practice' applies sometimes to learning to play cooperatively with different kids. They aren't best friends now, but play well together.
