Explaining to siblings

Hello. My middle child, almost 6, has Asperger's Syndrome. I have been trying to explain in developmental appropriate language her condition to her and to her siblings (brother - 4, and sister - almost 7). I have searched and found one picture book; but even those are hard because not all people with Asperger's display the same behaviors. Does anyone have any suggestions on how to explain to siblings and help them learn compassion and how to have a relationship with their sibling with Asperger's?