They were all under the one E Visa account. Mine was submitted one day prior to the other two. I did not need to wait for my approval prior to my wife (dependant) being approved. So yes having them on the one account seemed to work as far as the Thai consulate identifying that there were connected. All three came through approved at the same time.
I’ve heard that he can not as he is not my biological son. He is my wife’s son of her previous marriage. Would make life allot easier if he could be classed as a dependent