I'm so sorry SloRian, what a horrible situation for you and your children. Other have said some very wise things, but I wanted to give you my support and say that you are a strong woman, and you would cope with a big change no matter what. It might be hard and emotional, but if you needed to go it alone I believe you would do ok.
Think now much of your strength and emotional energy is being spent at the moment in containing his anger and emotional garbage... It sounds as though you are going along behind every move he makes, trying to minimize the damage and hurt he is causing. It must be exhausting and distressing to be doing that every day, and to not be able to share your worries and fears with the one person you should be able to rely on and be in a partnership with - your husband.
I would never say 'leave him', because I don't really know you or your life, but what you're describing does not sound good, and from your post I think you are well aware of that. I've got friends who had bad relationships themselves, or whose parents split up, and they all spoke of the relief when it was over and how they hadn't realised how badly it was affecting them until afterwards. Sometimes things just don't work out, and it's not your fault if that happens with your family, because it's clear where the problem mainly lies.
Being brutally honest here, he sounds like a bully. When you said he is a decent bloke underneath it really broke my heart, because that's the way it always is with some people who have learnt how to bully and manipulate those around them. They can be lovely when they choose, but also horrible for no reason or for tiny infringements of whatever their 'rules' are. That's emotional abuse, and you and your children are being bullied in your own home. I know you said he hasn't been physically violent, but unfortunately that day might come if he has clear anger issues that are well known to his family. And if it did, he would initially be full of guilt and excuse himself, and you would want to believe him.... Sadly it's a pattern that is very well known.
The fact that your daughter said she wished you would divorce is very sad and chilling. Normally children will endure much to keep their family together, and she is clearly very unhappy to be saying that to you. Given that both you and she are suffering from CRPS, and your son is also suffering, the stress of your home situation must be making things worse for all of you.
Only you can decide how to deal with this, but although I believe counselling can be very powerful, I do doubt it's power to change behaviours your husband has maybe been using his whole life. I really really admire how you've stuck in there and refused to give up on the life you've built, but five years is a very long time to live with things this bad, especially in the life of a child. As one of the other posters said, children learn how to behave as adults from seeing the relationship of their parents, and what your daughter and son see at home will shape their own adult relationships. He is teaching them that it's excusable for a man to behave like this and make people unhappy, and that it's normal for a woman to have to excuse it despite her own unhappiness. That's a dangerous mix to try and deal with when attempting to find your own partner. Will your daughter recognise bullying or abusive behaviour in a boyfriend as that, or will she think it's normal and blame herself for a man's attitude towards her?
We all have doubts and periods of unhappiness, and it's difficult to know where to draw that line that says enough, no more. Your family as a whole has suffered so much, and of course that has affected everyone. It's impossible for anyone outside your life to know whether this is a bad patch, or a worsening situation.
From what you describe, I am worried for you, although I do hope that this counselling can finally change things. Even a small improvement is good, as long as your life together becomes something positive. Only you can decide whether that is something you want for you as a family. Maybe you could consider a trial separation, maybe he does need a proper wake-up call, maybe as long as you are all there he feels it can't be that bad. Or maybe it will get better, maybe the counselling will change his behaviour, maybe you can all start being in the same room together without the tension and fear...
I wish you all the luck in the world. You have been very strong and supportive of other people on the site, and always positive and cheerful. It must have taken a lot for you to make this post, and I think it's an amazing step to take.
Take care of yourself and remember that we are here for you, and want you to be happy.
Bram