I think the best approach I have learned, is that I cannot get him to co-operate, in any way at all, that in the end this is his lawyer's job, and that fact will drag this divorce out and make it more expensive for both of us. We can no more have a reasonable grown-up divorce than we could have a reasonable grown-up marriage. If I accept that this is the way it will be, at least I am not stressed about it too.
My stbx spent months refusing to acknowledge lawyers letters etc but has now decided that since he has got his info together finally, I should jump to it and get mine sorted out in double quick order. He variously suggests, agrees to and then withdraws, reverses settlement arrangements. In order to remain sane I take no notice of anything he says, nor will I take as red anything that he agrees until it has been signed and agreed by a judge. He often threatens to do things that he legally cannot do, because he dooesn't understand the process of divorce nor the likely outcomes, I ignore all that too, I let my lawyer communicate with his lawyer, I pay her to negotiate, and that is what she will do.
did this feel like I was pointlessly lining lawyer's pockets when it all could be avoided if he were able to communciate reasonably and remember and understand stuff? yep.
can he communicate reasonably and remember and understand stuff? nope; so money well spent.