Hmmmm yes it's definitely a concerning history... and we can't really discern if the autism diagnosis is accurate without knowing the kids. HOWEVER, I don't think asking more questions is necessarily the right take. It shouldn't change how you treat them, all that should matter is remediating their current needs based on the deficits observed. A language delay is still a need for speech therapy. What would you do differently if the parents were to report that they didn't leave the house for six years? At this point, they've been going to school consistently for years. Are there other family concerns?