Look, sounds like you're lovely and everything,but he's completely taking the mickey.
1. He completely messed up YOUR life with his A and you have worked hard to put it back together. He has made poor choices and the state of his life right now is as a result of his choices. It is not your job to fix that.
2.Not only that,you've had to do so without the Cs that he should have been paying all this time. He has spent that money over those years on himself,he could have chosen to pay it, but did not. Now he is reaping the consequences of his choices. It is not your job to fix that.
3. He is using emotional blackmail on you and the children. If you let him get away with that,you are teaching him AND YOUR CHILDREN that it works and he will keep doing it. It is not your job to pander or reinforce his poor parenting/people skills. It is your job to set a good example to your children of how to stand up to emotional bullying.
4. He is disrespecting boundaries,especially yours. You're worried that you have to reply. No. You need to enforce your own boundaries and teach your children what healthy boundaries look like-they need one parent who can do that.
If you REALLY feel you need to reply, copy in your attorney and simply say:
Do not contact me about this any more. If you need to feel the need to communicate,please contact my attorney