I had similar to this 18m ago, but my son was 8.
It was terrifying - mum and her h wouldn't leave either, I had to call the police.
There's never been any apology, or acknowledgment of what they did. I'm NC now and it's better.
Their bullying of us started when my ex left too, it's called putting the boot in, kicking you when you are down,
Now that your relationship has gone, THEIRS IS The worst, so they exploit you to make themselves feel better.
I'm glad your exh is coming over, I hope he is helpful.
Fwiw, if I were him I'd withdraw permission for the holiday, no you need to be proactive on this and refuse to go.
You need to get your do and her h out of your lives, you're not safe with them in it.
You did a great job of protecting your ds today. Well done