From my experience, you can't negotiate with a narcissist.
Just present the facts, and don't go forward until he clarifies stuff like where he got the down payment for the house. Like bank statements for the past 3 years, pre and post separation. Like a complete credit report that reveals all his business transactions. There is always a trail when money is moved.
Get a tougher lawyer. Yes, really. Look for a junk yard dog who knows how to bark/bite at his kneecaps. Nice comes later when he's agreed to reasonable stuff.
Get tougher. You can't make him happy, so make it all real. If he gets upset, that is probably what he intended to do anyway, and at least you get your points made.
Like many of us were with narcissistic spouses, you sound intimidated. Get over it. He is on the way out of your life, like a passing wave that has brought up all the debris from the ocean bottom.
Say what you want, and just don't budge. "No." is a complete sentence. To be followed by a very very long pause that eventually he won't be able to resist filling. Then "No." again. Then after the tantrum, walk out. No sense wasting lawyer fees when he is just spewing nonsense.
This man is now not your husband, your lover, your protector. He is not planning to help you. He is an adversary. No more, no less. Leave the emotions behind, and sort out what you really need to be free, and then go. Our hearts can mourn on our own time; negotiation time is purely that.
There is life on the other side of narcissism. Very good life, and it is waiting for you.
ShootingStar1