I remember your last thread.
It seems to me that your MIL is the real issue. It's the one you keep coming back to in your threads- and quite rightly, after what she's done. I think that this is the thing you have to tackle. I think this is the thing that is making you feel miserable and under threat.
Not that your mum isn't an issue - but the situation there is very clear cut, and you have put in place boundaries to stop any contact, which is absolutely the right thing to do. Your mum is of course the founding issue, but she can't do anything or be a part of your life, and that is right, and you are in control of it.
But in MIL you have someone who should be absolutely on your side, and who has betrayed you. Really badly. Her hideous, false sentimentality - 'mother to mother' - to a woman she doesn't know and who is it seems the antithesis of motherhood - how dare she? And how dare she take it upon herself to dismantle the boundaries YOU have placed around YOUR family on this issue? I am not surprised that you are having difficulty getting past what MIL has done. I wouldn't be able to, and I would have had to cut contact with her, at least temporarily. And I would have demanded to know what she had said, done, sent in full.
But from your previous posts I see that you feel you can't do this. You want MIL to like you, you don't want to rock the boat. And you are intelligent enough to see that some of this neediness comes from your previous mistreatment and the scars it has left. So, MIL is hurting you on another front - this issue highlights the fact that you feel that at some level, you can't stick up for yourself. While MIL swans into your family unit and makes you feel as if you don't even have control of that.
I think you need to sit down with your DH and talk to him in depth about this. Then he, and you if possible, need to speak to MIL and say that actually, the effects of her actions aren't in the past. You've tried very hard to get past them for her sake, but you can't. You simply don't trust her anymore and cannot understand how she could possibly side with an abuser against you, her son and her grandchildren. (Yes, that's what she's done - make that clear). And that you need to cut contact for a while until you BOTH decide whether you can have her in your lives, or whether given her actions it is better now to go your separate ways. And say that if she has anything else to say, it would be a good thing if she could confess it now. Has she sent anything to your mother - photos etc. You both need to know that now.
She will cack herself. And that's the intended outcome. She's behaved despicably. She needs a sharp wake-up, not only so that you get back the control you need within your family, but so that she never even considers doing anything like this again. I think that this is the ONLY way you are going to find some peace here. And you don't have the strength right now to do this yourself (nor should you - it is an issue for you to face as a family) so your DH needs to help you. He also needs to be the front runner here so that YOU do not get blamed unreasonably for something that MIL has had coming to her for quite a while.
I assume you wouldn't want to cut her off forever, but it would not only give you a break from her, but also maybe tip the balance of power in your favour a bit. It's good that you want to be on good terms with her, but NOT good that you feel so... needy about it, unable to be in charge of your own family boundaries. It's quite likely that she's sensed that, and at some level that's facilitated her interfering - that you're a poor helpless thing that just needs a nudge in the right direction. NO. You are not. You are an adult and have your own nuclear family now. You don't need to get on with her at the expense of your own peace of mind.
Good luck. I really hope this works out. I can see where you are coming from entirely.