I agree to contacting gorgeous man. If you don't get back in touch that's another potential loss due to all this unfairness. I'm sure he must know that the outcomes can be very unfavourable, you will be a knowledgeable support for him.
I see they were 3 JP's not judges. Well, I think that explains a lot. I've known some family friends who became JPs. With the exception of one, they were all small minded bigots who I wouldn't want to judge a beauty contest 
I agree with the previous comments about how to be honest about your ex without bad mouthing him. I never just start saying bad things about him. I also still say if I think he was in the right. For example, they described a situation last weekend where he was cross with them about something. I said that based upon what they told me that was fair, I would have felt cross too.
What I don't do is try and make it all better. When my ds said last week that he thought they always did what dad wanted to do, I said "Do you, yeah, I can see that would probably happen." When my dd said her dad couldn't come to something that was important to her because he had something very important to do, I scoffed. I asked her what was more important? I don't think that's bad mouthing.
If we're not honest I think it's a form of gas lighting, unwittingly. The dc will think "my mum doesn't think it's ok when other people say that" or "I know that's not true but my mum is saying it is". I think that'll really mess them up.
I totally agree with greencar saying that you don't want them turning round in 10 years saying why didn't you warn/tell me ? That's why I've told them what their gf has done. Imagine thinking he was a lovely cuddly gf and finding out later he was a bastard who'd largely destroyed your family. They know (a child friendly version) of that already. So, they are forearmed and he doesn't get two adoring gc. That's fair in my book, and I'd defend it if I had to.
Part of the situation regarding my break up involved members of my extended family. I had known and trusted them my whole life. They acted in a way that made me feel like I had never known them. It shook my world, and I would do anything to protect my dc from that.