If she has filed for a modification of the property settlement, then your son needs to be working with a local attorney to respond to it. No one here, however, can predict how a judge will rule on her modification or your son's response.
Your son does have a responsibility to refinance under the circumstances, even if it's not spelled out in the divorce/annulment agreement (it should have been). The fact that his ex-wife is still on the mortgage could be preventing her from her from obtaining credit and moving on financially as well. Your son can't blame her about the refinancing situation -- he's an adult and shares the responsibility here.
Finally, there is no "we" in this situation. You need to stand back and let your son take care of his own affairs.