Welcome! (back)
You asked, so I'm going to give you my "expert" opinion. I agree with your ex and the doctors that the ODD diagnosis does not need to be there. Seriously. It just means your kid is REALLY difficult, but doesn't explain why. It doesn't offer any sort of treatment plan, or explanation of the behavior.
I also agree with you that there is more than ADHD going on.
Unfortunately, that's all I can say given' your situation and what you've shared. I'm in the process of divorce and have custody of my kids. FH hasn't made any attempt to see them in years and doesn't even know his kids are on medication. The man has NEVER asked how the kids are doing, so I don't feel obliged to tell him. Especially since when I was volunteering the information, he ignored it all.
Having said that, it seems like your son has 3 adults to take care of him. Risperdal may be decent medication for him, but it IS very heavy duty stuff. And yeah, it was causing a very undesirable side effects. There are other medications out there that may work even better, but no one is looking for them because the adults are arguing. in my opinion, you're right and ex is right and you are butting heads, but at the same time you are both wrong but refusing to back down from your "right" positions and not exploring where you both are wrong - the 'something else' that is part of difficult child's diagnosis (maybe several 'something else' s.)