Here are some general approaches we've found that help families dealing with Asperger Syndrome and autism:
Be open about a diagnosis and what it means. Parents tend to assume siblings know more about Asperger Syndrome and autism than they actually do. Explaining to extended family the reasons for a child's behaviors and how to react lays the groundwork for positive family gatherings.
Treat children with special needs as children first, not just as patients.
Give time and attention to each child in a family. This will be more helpful to a special needs child than focusing on him or her to the point that siblings feel neglected.
Find activities that family members (especially siblings) enjoy doing together.
Take care of the caregivers. Most parents (and other caregivers) need to take some time for themselves to take the best possible care of children.
Reach outside for help when necessary. Support groups and counselors can offer approaches and solutions that families may not think of on their own.