Yes, I agree it sounds so familiar. They have no conception of what D is all about. They feel *trapped* and *controlled* and they just want OUT.
I hate to say it but it sounds like he will push the D through. He somehow *needs* to. I don't fully understand that but my stbxW is the same way. Their thinking is that if we would just go away everything will be fine. They really do not think anything bad is happening - this is best for everyone. That is also why they try to be friendly towards us and treat the family and kids as though nothing is happening.
Do grill your lawyer and understand your position. Mediation is fine but the *legal* D is cold business now. Protect yourself and D6. If he pushes through then work with him best you can but don't give up anything that you are entitled to. Much of D is cruel but you must be strong. Do develop a comprehensive parenting plan in addition to the settlement division.
As for the *emotional* D, it does not hurt to use DB, especially showing him what life will be like without you. From your writeup it sounds like he is no longer living with you. If that is so, make it clear he is no longer welcome (although legally you may not be able to keep him from the home). Have little contact. It most likely will not wake him up, but it will benefit you - to work on your life and emotional state.