I empathize with your situation. I have a controlling ex, and have been divorced around 5 years now.
He is going to try to keep controlling your life. He is going to be a pain.
I have to be careful not to be too friendly or nice with mine, because to him that's an opening to exploit.
You will have to decide what hill you will die on - in other words, what decisions are so important that they'll be worth the conflict caused (and stress to you and your children) by doing it?
Mine has been coaching my son on what to say for a number of years, now. If we go back to court, my son is older now and will probably repeat what his dad tells him to. I will likely be screwed. These are the type of antics you might have to deal with. And the court may not end up caring about them, unless you can prove things beyond a shadow of a doubt, and that requires you to dwell on the unhealthy aspects of your life a lot.
My advice is mainly this - say no only when it's very important to you. Then, stick to it. Don't be too friendly with your ex - it might seem like it's best for the kids, but in the long run, if he's controlling, it will hurt you (he will likely still think you're the same woman he has pushed around for however many years). Try not to sweat the small things, no matter how upsetting they are. Don't engage him - don't ever fight or argue. State your decision, tell him the reasons why, and walk away.
Having a case manager, in the long term, can help a lot - they can unofficially do things. My ex wouldn't allow me to pick up our son once, and I didn't call the police, but I did call the case manager who told him to cut it out. It does help, to an extent.
More than anything, you have to be strong in a way that you didn't before. But, you're sticking up for your kids, so that will make it easier.
Best of luck to you during this time, I'm sure you will get through it! On the plus side, you can practice being assertive with your ex, and then you're all prepared for being assertive in the real world!