Wow, thank you so much for such a comprehensive reply Threesocks! You have really put our minds at rest, and given us some good places to look for information, am so grateful.
I will do the course, I've arranged my hours at a new job I'll be starting soon to allow for it - the psychologist who has referred us and who will be running it is coming out next week, so I'll talk through my concerns with her, hopefully I'll be able to start it in a better frame of mind. I can see that she can't be expected to keep coming out to us individually for the long term and I think we've been really fortunate to receive the support we have so far, so I don't want to get off side with anyone. She mentioned theraplay, but I think this would only come in after the course is complete, I have a friend who did and recommends it though.
Fortunately school have applied for temporary funding this week for a fulltime one-to-one worker for DS and are working on an Education and Health Care Plan for him, hopefully will be in place in the spring term. The staff have had attachment training, and also the Ed Psych got them onto a Louise Bomber book, think it was a different title to the one you mentioned but was in a similar vein, we had it too.
I've been on an attachment training too, but it was about identifying different attachment styles with no info on how to parent a child with any of the styles talked about.
I think DSs mega meltdown and exclusion have brought things to a head - he had psychological testing recently around empathy and ability to inhibit his own behaviours, but the results were not shared until this week - until then there were a few different theories about what the issue was, so now we have a clearer pathway. I think me and DH are accepting that we have DS with SEN now, rather than a boisterous little boy, so that feels a bit strange at the moment, but at least we've got a clearer way ahead now. Feel sad for DS, DD misses out on attention because of how he can be, but we'll find ways of managing things better now hopefully.
Funnily enough, I've seen lots of mentions of the Ross Greene book, but have steered clear and stuck to Webster-Stratton, but having just had a look at the website his approach makes a lot more sense for us, so I shall be getting a copy.
I did yoga for several years and I do use it in little ways with him - sometimes my mummy instincts are right after all. And I'll get back onto the Omega 3, I was giving it to them both for a while, but haven't lately.
My big problem is dealing with feelings of guilt that my parenting has been the cause of all this, although I can honestly say I have done my best. I feel so very guilty that I've turned my lovely baby into a troubled child. The stuff about attachment often sites inconsistent parenting and neglect as causes and I feel awful, but I can't really see that I got it so wrong.
I would LOVE a Mumsnet book of Extreme Parenting, I could add lots of amusing tales of what eccentric things my LOs have got upto 
Thank you very, very much.