In this video which discusses the single child vs siblings, Dayna Lim narrates how an autistic child can grow and develop differently with and without siblings.
She pointed out on how a child on the spectrum will benefit from both different scenarios.
In this post junior school series, Dayna touches on how teenagers will have a closer-to-age role model which is important for their new identity development if they have a sibling for them to emulate.
There are no best answers to how a family structure should be as every family dynamic is different.