If he has an attorney, which he does, it seems, they'd doubtless be feeding him information. If he's on any of the numberless websites that do so, other people getting divorced may be feeding him information too. If he's reading case law, that may be feeding him information. What I'm saying is that your soon to be ex husband may very well be obtaining all the information he can, and he is a free agent in this case. Of course he can rightfully do this.
I'm very curious about the 12 hour mediation session. So you started at 8:00am and finished at 8:00pm? I can hardly believe that a mediator would agree do a session like this, though it would probably be cheaper if they were being paid per session instead of per hour. It is legitimate, though it was probably very unpleasant. But from the sound of this, your husband wants this to go on through. And there's no obligation or insistence that you have counseling or try to work things out.
Try in all sorts of ways, to keep things civil and smoothly operating in the interests of your child. Why did you not have an attorney in the first place? It may be costly to hire the attorney who said they "might" be able to change some of the mediation agreements, from what I hear, you've consulted about three attorneys who have not told you anything you wished to hear.