I also can see the possibility of autistic traits, but there are other possibilities too beyond autism. We can't diagnose here, MWM is correct. However, you can have a peek at
www.childbrain.com and look for their informal online Pervasive Developmental Disorder (PDD) questionnaire. Run it on him yourself, see what you get. Print it out, maybe discuss it (or do it with) your husband, see what he says. Denial is more than a river in Egypt!
But seriously - if neither parent will accept there is a problem, there really isn't much you can do other than reactive, rather than proactive.
Going over what you describe -
1) The custody split/arrangements will be unsettling, especially if he has autism in any form. It certainly won't be helping.
2) If there is any instability in the mother, this could be aggravating things in terms of genetic causes, as well as in terms of challenging behaviours he is exposed to and which are being modelled for him. Substance abuse in other family members can indicate a family history of underlying disordersfor which some people self-medicate with substance abuse.
3) His early history - language delay can be a sign of autism. So can delays in other areas but they can also be signs of other things, including a disrupted home life. Quiet solitary play can be a sign of a lot of things including within the range of normality.
4) Gagging on food that he knows you've cooked - this could be coming from bio-mom and her attitude to you. Again, this still could be under the autism umbrella because autistic kids can be intensely loyal, and if his mother is sending him messages that to publicly reject you is to show loyalty to his mother, then this could be where it's coming from. She needn't be telling him to do this, it's just what he has worked out for himself. These kids develop their own rules if none are given to them that they accept. They are VERY law-abiding, just not always the laws we want. Often it's the laws they assess for temselves as being the ones that seem to explain the world in which they live.
5) The assessment - too short, too brief, the girl probably too inexperienced. But the results still could be a useful starting point for a later, more thorough Auditory Processing Disorders (APD) expert assessment. He needs one.
6) Always wanting to play the villain - I wouldn't be too concerned. It could be a good sign on a number of levels, because being able to participate in imaginary play is unsual (not impossible though) for someone with autism. And easy child used to always choose to play villains, because she said they were far more interesting, much more fun and she got to indulge in a form of legal naughtiness, being permitted to be evil if it was just a character she was playing. It helped her get her hostility out in a way that was more acceptable. For example in a dance concert of "Lion King" she adored playing Scar. In pantomimes, she insisted on playing the wicked witch.
In this one, dad could be right - it could just be "boy" stuff. Or it could also be his way of trying to release a lot of confusion and hostility (he sounds like he has a lot, even a easy child would struggle).
But the other stuff - yep. I tihnk you're right to be concerned.
Would your husband read posts here? Would it help him do you think? My husband does, he has joined the site with his own ID and even though we have always communnicated well, now we're even more on the same page than we thought possible.
Marg