First, I'd recommend Al-Anon for you. It is a tremendous support system for those who have been unfortunate enough to end up loving an addict.
Second, he's WORKING on his 4th step? How long does he plan to do that? The 4th step should be a fairly short one, as it's task-based. He should clear his schedule, start writing, and shouldn't stop until he's done. He should not expect it to be perfect, just as honest as he can be. It's progress, not perfection, and he can do another one later when he has a greater capacity to be honest.
I feel it is the most important and also the most difficult of the 12 steps. Mine wrung me out, but I needed to do it if I was going to survive. And when I shared it in Step 5 with my sponsor, I had a spiritual awakening that changed my life forever. It was one of those "nothing changed and everything changed" moments in my life.
The 4th step is the "5 minutes before the miracle" time. He should NOT quit 5 minutes before the miracle!
It sounds like he's trying a bunch of different things, hoping something sticks. That's good. NPD and addiction are both very hard to recover from; both require changing long-term dysfunctional coping mechanisms that worked for him for a long time.
Dual diagnoses are a tough hill to climb. But not impossible. I was addicted to alcohol and had GAD, but I sacked up and got through both, so it can happen. I'm nothing special, so yeah, it can happen.
If he's brave enough to be really honest with himself, he has a chance. He has the potential to have an awesome life that he never imagined he could have.
He shouldn't worry about deserving it or not, because if we addicts look at it objectively, we already don't deserve to be here at all, but our higher power is giving us the opportunity to recover. He should NOT squander that opportunity.