OK, some major progress (I think), though am still wary of whatever that woman says to me.
Long story, here goes...
I rang the LEA this morning, to ask if and how I can find out if and when he was placed on E(nhanced)EYAP, I explained the very outlines of the situation we are in, she said she'd talk to the relevent person and get them to ring me.
Next conversation I had was with the HV, I wanted to tell her what had gone on yesterday at the meeting, although sometimes it seems she can jump the gun a little, she is our biggest advocate so far, so I really want her to be kept in the loop at all times. She was disgusted that the SENCo had laughed off the SA, she agreed totally with the outline of the letter I told her, she is going to ring me back with an appointment for his Paed, hopefully for Friday, but we'll have to see. She has suggested bringing the next TAC meeting forward from May, which can only be a good thing. Also, as an almost aside issue, a couple of weeks ago Portage came to do an initial assessment of DS3, my HV knows the Portage team very well, and socialises with a lot of them, now apparently, the two Portage workers that came have said to the HV that when they arrived, they couldn't tell which child they'd come to see, I asked in what sense, and she said they couldn't tell which of the children needed the therapy, which means that they saw something in DS2, problem being, it is all off the record, can't be used. But it does back up my theory of this facade he puts on socially because due to circumstances with people being off sick, I knew that one of the workers would be a man, but I didn't know if the second worker would be the HV (who DS2 loves to bits) or if it would be a stranger to DS2, as it was, it was a stranger, so for that little while, while they were coming in etc. he didn't know how to handle it. And they are probably the ones to have seen DS2, just as he is since the HV first met him.
Then the promised phone call to find out when he had been placed on EEYAP. Interestingly, it was none other than the area SENCo! She explained that DS2 would have been placed on EYAP as soon as he started with the nursery, she admitted we should have been informed of this, and that we should have been involved with targets, observations etc. She is saying now they will apply for EEYAP, which is basically the funding for teacher assisstance, which will allow her to carry on assessing DS2. I didn't really want to go through my feelings with the nursery SENCo, but didn't have a lot of choice as apparently she'd been told I wasn't happy (by who?) so I went through some of the points, not all, she said alongside the nursery SENCo, she hasn't seen any area's where DS2 is in need of additional help, however she has only observed him once, and she is very happy to keep going back to see him to see if she can pick up on anything in the future. She offered to put forward the request for a SA, and I declined saying I'd do it. I think by the time we finished talking she was really quite cross with the nursery SENCo, and I was fully expecting the next phone call...
Yep, nursery SENCo, she has completely changed her tune, she never actually came out and admitted he does have additional needs, but then I was never expecting her to after what's gone on, but she apologised for us not being informed/involved re. targets etc. also offered to do the SA (with almost the exact same wording as the area SENCo used, and when I said that I'd do it, they both then went on to offer help on finding me the forms etc. which I thought was a little strange.) she made it very clear that she thinks the things nursery have done so far have been quicker than things would usually move (what, 4 months to write him some targets? And what else have they done?) I have asked for her observation notes and reviews to see how he is progressing, there is going to be nothing outstanding though, she said she'll get his file ready for me to see, but that it is only the same observations she would do for all the children at nursery.
And low and behold when I went to pick him up from nursery, she was there, I have never seen her there twice within such a short time period, am sure she thought she'd get somewhere with me face to face, but I complete overlooked the fact that we'd spoken this morning, didn't engage with her really at all, while she was being all lovely and helpful 
So, some progress, at least they know I'm not going to roll over and take it, and even if they do nothing now, it will all be backed up in writing, and I can get on with the SA.
Don't make it bloody easy do they?!