Hi again, OP. Glad your DCs are home and so sorry that you've had such a horrible weekend. Sorry also that your thread has been dogged with so many people who can't be bothered to read it properly, and now also has been overrun by what Hissy has excellently described as 'blow ins from Gransnet'. I am also a mother of boys and have no worries whatsoever about them getting married, as I have absolutely no fucking intention of behaving like these dreadful matriarch MILs who treat their sons like a battleground and their grandchildren like the spoils.
My own MIL showed her cards nice and early by being on holiday for the first three days of DC1's life, and then phoning on day 4, when my milk had just come in and I was a sobbing, leaking, bleeding, gibbering wreck, and announcing that she was coming over immediately. When asked to wait 24 hours, she responded by bursting into tears herself and having to hand to phone to FIL as she was 'too upset to speak'. She did, however, manage to wail 'Why, oh, why are they trying to keep me away from the babyyyyyy!' so loudly that it could be heard openly in the room at our end. All of this was a complete departure from her previously reasonably civilised behaviour, but has been replicated again and again in myriad ways. I have kept her on a fairly tight rein, as I regard her as unhinged where the GCs are concerned, but she has still managed some proper outrages over the years when the supervision has slipped - I could give some corking examples, but they would totally out me!
So your situation is not at all uncommon, OP, however singled out and victimised you are probably feeling atm. It's also well-worn territory that your DH can't see his mother's behaviour for what it is. He has obviously learned from the earliest age that the fallout when mama doesn't get her own way just isn't worth it, and probably filters what he sees and how he sees it through a lens that helps him put her first in all things. FIL is probably an enabler, siblings may well be ranked in order of how well they meet her needs, etc, etc. And then along comes you. You are right that she feels threatened by you. You have the power to unseat her from her position of supremacy, because the smallest additions to the family are under your direct control and are conditioned to be loyal to you. You are also going against what she sees as the natural order of things if you challenge her at all, because she may well have lost a similar battle of wills with her own MIL, and so on. Women in generations gone by had very little power beyond the family; she has probably waited for the top job for a long while and doesn't feel like power sharing now she's got it.
What is tougher for you is that your DH is very hostile to accepting that her behaviour is problematic, and prefers to see you as the villain. There is lots of reading you could share with him - the Toxic Parents/Inlaws books, for instance, and myriad websites that others will no doubt point you to - and if he can accept that she is the problem here, lots of strategies you can use together that minimise the impact on him of having to stand up to her directly, e.g. deferring decisionmaking til you can 'check your diary', or taking the initiative to invite the PILs to your home turf to see the GCs so you avoid power struggles on their turf but give everyone their pound of flesh.
If he prefers to see you as the problem instead of her, though - and it sounds as though he has been really hateful to you this weekend - then you really do have a problem of a different sort on your hands. It sounds like revisiting counselling is essential - but do you even want to? DP and I have had numerous words over the years about the ILs' behaviour, how to view it and how to handle it, but he has never described my parenting as 'disgusting' or 'unforgivable', and never would. How do you get past that? Is this the only aspect of your relationship that is a problem? I hope there are other MNetters whose MILs have really tried to break up their marriages who have constructive advice to give and happy endings to share.
I really feel for you, OP. Power struggles are perhaps the most upsetting part of life. It is really tough when they are part of the landscape of your family, and unbearable in a marriage. 