As others have said it is probably time for you to play a little hardball of your own. Don't budge on that additional $3,000.00 you aren't here to make the deal convenient for them but for you and your son. It may come down to you may have to walk away from this house and find another. Buying a home in a divorce situation can be a very tricky situation for the buyer as well as buying a house that may be in foreclosure.
If you already have legal represenation for your closing, then I would let my attorney handle dealing with WF's attorney's.
This could go either way. You could close and this house with your FHA mortgage or not close on this house at all. The attorney may be able to help you recover some portion of the inspection fee's you paid because the bank would have effectively killed the deal with their ridgid ways.
While his house may have been perfect, it isn't the only perfect house and be prepared to shake the dust off and keep it moving if you need to.
In house buying sometimes you have to kiss a lot of frogs before you find your handsome prince.