I am sorry to hear you are "hitting a brick wall". I know before my husband and I were tested the drs said one of Us could have it and I then it would just be "normal" for our daughter. I am not saying this to you, I think you should continue to watch your son carefully. If he does anything differently or becomes unhealthy in any way bring up the duplication.
It took me two and a half years and several doctors ( multiple hospitals) to get someone to listen that my child had problems. And I needed answers and guidance.
Sadly answers are hard to come by just yet. However global delay and sensory issues are probably the symptom of his duplication.I was told some things do not change until puberty.
If I come across any info I will pass it along to you!