There are a lot of hoops to be jumped through before a nod is given for immigration to Australia. (I've traversed the holiday, business, fiance and permanent residency visa landscapes for my (now) husband and later, for his two daughters, utilizing both my own research and the services of a Migration expert.) One can't just 'decide' to emigrate to Australia.
Mum may have had the required skills points (being a nurse) and would also have prior marriage to an Australian resident in her favour. The three boys would have birthright status - however, there are very stringent protocols in place before granting a permanent residency: existing health conditions must be declared and health examinations are a pre-requisite.
What I'm suggesting here is that the label 'autistic' by an overseas relative may be a sweeping (and ill-informed) generalisation used to explain the 'odd' and reclusive behaviour of VS. The source says 'autism runs in the family.' In that case, documented medical evidence, disclosure at time of application for immigration and subsequent health assessment is mandatory.
Lots of people are anti-social, perceived as 'odd', reclusive and subject to angry outbursts of frustration at not being able to keep up with a peer group. A nine-year-old losing his cool in the classroom and 'attacking' a teacher does not necessarily indicate autism. It may also indicate simple frustration on the part of the child.
There are many, many documented cases of parents with a genuinely autistic child not being allowed into Australia (as unfair as this may sound) as the child is perceived to be a financial drain on already-stretched resources.
I'm not saying VS does not exhibit some traits of being on the autism spectrum: what I am saying, is that if this had already been picked up, (as indicated by the overseas relative and apparently accepted as common knowledge) it would have to have been declared at application time.
The other thing with immigration eligibility to Australia: even with all the points required for a particular skill-set, you would normally have to have a job to go to. You would also have to show you can support yourself and your dependents - or that those dependents were capable of employment, or you could bring in thousands of dollars to the economy. (Of the latter, clearly, the Stanford family did not.)
The genuinely medically-diagnosed autistic children I know are sweet, loving, gentle people who would never even think of hurting anyone.
Sorry, I guess I'm objecting to people who bandy around the word 'autism' as some kind of rationale.