I understand where you are coming from, but from a legal perspective, I can see a lot of components of your case that may prove challenging.
The first is that you've based the suspension of time on one incident and an expired AVO. Was the father ever convicted of breaching the AVO?
The court knows couples fight, and parents who are still together and fight in front of the kids aren't about to lose their kids to DHS just because they argue. It's unfortunate, but also an unavoidable reality, and the only difference is that he fights with his current partner in front of the kids, instead of with you in front of the kids. It's not ideal, of course, but unless there is evidence that the kids are at direct risk of harm, the court won't agree with suspending their time with their dad. Doing so is ordinarily perceived as just as destructive as exposure to conflict.
The second challenge is that, insofar as I can see, you have not witnessed the violence between your ex and his partner for yourself, so you have no genuine way of knowing if the kids genuinely were in harm's way. You've instead made that assertion based on comments from minors far too young to give credible evidence in court.
The third challenge is the assumption that your son's behaviour is a direct result of seeing his father fight with his current partner. Unless you have expert evidence that can be tested under oath and cross-examination and still support that assertion, it is unlikely to hold up in court.
The fourth issue you might face is encouraging the father to have a relationship with the kids. That's the wrong way around, in terms of legal matters. It's encouraging the kids to have a relationship with their father that's important, and I say this because parents are in very swiftly growing numbers losing residency of their children because there seems to be some confusion about what 'supporting the relationship' actually means.
I am sorry if this seems somewhat blunt. I'm merely trying to give you an idea of what kind of challenge you may face in a court hearing. Court is blunt, and they are very frequently harsh with parents who unilaterally suspend time between parent and child. The court depends only on facts and evidence, tried and tested under cross-examination, to make its rulings, and without evidence that the children were directly in harm's way, you may be facing an uphill battle.
If nothing else, I hope you interpret my commentary as insight about what the other party may pitch in their argument.