I had simillar problems with my son, we went through pretty much the same thing, untill one day a ENT asked about his sleeping habits, "what he's like when he's asleep"? He used to snore very loudly and several times during the night his breathing would stop briefly. As it turned out he had Obstructive Sleep Apnea, by removing his Tonsils and Adenoids this help greatly, he's now progressing great and most of the problems we had have been sorted out. It may be worthwhile looking into it.
Kathy
Dear Ms. Hale,
From your description, there is no indication that your nephew displays an emotional or mental disorder. However, there are indications of speech/language problems, as well as neurointegrative problems. Speech/Language evaluations are pretty structured exercises, and should, at your nephew's age, pinpoint the precise nature of his deficits. If it's been some time since his last Speech/Language evaluation, a repeat would be in order. On the neurointegrative side of things, Occupational Therapy would be the correct route to explore possible Sensory Integration Disorder.
Now, it is possible that what the various evaluators have discerned is a general lag in development, with the notion that your nephew will progress just fine. But it is important to spell that out, if indeed that is what is being suggested.
Relative to your nephew's sleep, it's important that he not be allowed to sleep with his parents. The sleep/wake schedule should at his age be pretty established, and this may bear some examination. I can't comment beyond that, not knowing the specifics.