I'm sad that your wife went to a lawyer....I fear that divorcelawyers being what they are, you can't expect that the lawyer will try to convince her to give the marriage a try. It might not yet be too late to ask your W if she'd consider going to a theraputic mediator to iron out the finances, instead of an attorney. And although some here might think it not a good idea, I wonder if giving your W a copy of 'Divorce Busting' at this juncture might not wake her up to the other side of divorce. (Financially, it bodes not well for a woman, especially a young mom.)
As for MIL....how does she feel about marriage commitment and divorce in general. She could be a 'help' if your W doens't convince her that you were a cad in some way. But moms can also be very protective of their d's and especially their grandbabies.
I'm sad to see any marriage fail. I consider divorce a tragedy and destructive not only to the family, but really to our entire culture that we trivialize it so. Altho I haven't read many of your posts, I feel that you have been trying very hard to save your marriage. I'm sending pixie dust your way!