What you decribed these criteria are very severe cases

ASD has a very big range, and it could be as severe as you mentioned. However, it could be very mild. Most of autisic kids I have seen are in between, and very case by case.

I do think you should bring your son for an evaluation for good.

One big misunderstanding here are:这样的孩子对亲人和生人的反应没有很大的差别。
Most of these kids get very closed to their family, and they do play with their sibling(s).