Abusive ex

[brighteyesburninglikefire]

Has abused his current partner in front of my children. My daughter told me that during a visit to their new flat, he got hold of her wrist, she jumped with fright, and told,her to "watch it" apparently she looked afraid.
Also during the visit, they asked her if she was happy at her school, and wouldn't she rather go to a nicer one, does your mother feed you enough, and also told them repeatedly that his new gf is a better mother to them than I am. My youngest is autistic with learning disabilities and they told him this repeatedly.
How can I protect them from this?
There is no CAO in place. I'm not shocked by any of it, but I need to,arm myself against any attempts to seek custody of my daughter (especially her because he will ruin her life and push her into an arranged marriage, he has no interest in her brothers).

So I emailed the ex, asking him to give them more food in the future and to,be careful of how he phrases things, because the children are not happy.
His new partner emailed me, when my discussion was with him, and she appears to be defensive about all the complaints in your email to him.
He’s emotionally abusing her obviously, and twisting the communication into a criticism of her and her parenting efforts.
What can I do though?
I know what it is, I know what’s going on there, it’s obvious to me.
I hope she seeks help and gets away from him, but right now she is deep 8n the fog, and I have my children to protect
I can't get involved in that, it'll just drag me back again into the drama he creates