Need help with diagnosis/treatment options; everybody is stuck

Some details change to protect privacy, of course. Child under 10, bio mom did hard drugs during pregnancy, left child withdrawing after birth. Child has ADHD, possibly autism (waiting for neuropsych). Behaviors include: emotional dysregulation, poor impulse control, defiance towards current caregivers (relatives who have been there since birth, they're a great caregiver), lying, stealing, manipulating, anxiety, recent intrusive thoughts, etc. Previous physical aggression when dysregulated towards caregivers. Poor w/ boundaries. Caregivers are burnt out. At school, child is fine for most part.

I've been working with this child for 3 years now and have tried absolutely everything I can. I have researched so much. I have talked to supervisors. We've developed a million coping/regulation strategies, have developed a million ways to remember strategies, we've included the client in creating rules + consequences to have some sort of control, etc. I've worked with the parents. The parents are consistent and are trying their best. We've done some play therapy, too. Nothing.

The child has tried so many different medications but not much support from them. I'm just wondering if there is something I am missing? Of course, you guys don't know them so you can't get a good picture-- but based off of this, any idea?

Also, they have been aggressive towards animals as well when the animal hurts them in any way (accidentally scratches them, for example) (However, it is important to note they LOVE animals. They can talk about them for hours and how much they love them). When their caregiver accidentally hurts them, they're quick to be aggressive, too. I'm thinking maybe they have sensory challenges because there have been times where they've had a stomach ache and have banged their head against the wall so when they're hurt, it's 10x worse for them? I don't know. I'm just stuck!

They're diagnosed w/ ODD by their psychiatrist but that diagnosis is just so unhelpful and stigmatized and anything I've looked at online for it just says to mainly work w/ the parents but I have and NOTHING WORKS!