GettingStrong (yes, you are!), the fog is lifting now and you are feeling pain that was anaesthetised by just coping with such severe and comprehensive abuse, protecting your DC, and, yes, minimising. Part of thag will be accepting painful things about your actions BUT do not make this your focus. You know you have masochistic tendencies in terms of excessively blaming yourself, please do not use beating yourself up as the new thing you use as a displacement to not focus on what really needs to be focused. You didn't realise the full extent or effect, but you knew enough to get out, you reached out for help and you took it, and you're working through it now. You have changed your Dc's chances in life for the better, totally. Better late than never, sweetheart.
As others have said, SS do understand what happens in abusive relationships. They understand the panopticon effect of abuse (you become self-regulating to the 'rules' of the abuse to save yourself, so that things that might make someone in a non-abusive relationship say "fuck off, you must be joking!", would make you accept and agree to with little or no questioning or resistence). But the worst thing you could do is to minimise and excuse his behaviour towards you all, and go on and on about how guilty you feel, etc., out of misplaced guilt and loyalty. There is a balance between accepting your part in things and then implicating yourself. I say this because I worry you would do this (I get v guilt-stricken over stuff, and probably would do it myself).
They will be impressed that you have left him, although, as you know, once his abuse is logged, you would bring a shitstorm on your head if you went back to him.
And there's a reason why he is obsessed with avoiding outside agencies (even a plumber!) - he knows people will be horrified, disgusted, freaked out, angry, weirded out, whatever, be that someone checking out the danger rooms in your home or a counsellor hearing the true extent of his abuse. If you want to break the cycle for good, and truly save those girls for good, you need to speak up and speak out. Remember - the truth shall set you free.
Greatvto see you back, GS, and hope our answers help a bit. Don't forget to ask WA and your counsellor. That is what they are there for, after all. Please don't think you're bothering them or asking too much.