sixblairs,
First, Hi and welcome to PsychCentral.
I'm so sorry for what you and your family are going through. In my experience personality disorders are very tough to get out of. Don't have direct experience with Narcissistic disorder-- but, been going to therapy for 1½ years for my personality disorder and it's a slow process at best.
Don't mean to make it sound hopeless, I imagine if the person is really willing and has much support from others, then there could be hope. But narcissists usually don't think they are the ones that need the help-- so getting them to stick with therapy would be a big task- IMO.
Are you or your husband in therapy now? If he won't go, you might consider going yourself--- as getting some insight coping with all that is happening can help in your feeling more supported.

I wish you and your family well. t/c
mandy