I believe they haven't turned from God but are angry at him. I believe that's apart of the grieving. Along with betrayal many feelings to process. Later a guy at work was talking about how bad he felt in his divorce like a failure. I told him he should of felt success.
Just pray and be there for them. They will work through the process.

I'll pray your son and family,I do understand how he feels my husband was killed at 41 and our kids were 17 and 12. I stayed strong Infront of my kids and We also owned a drywall company I had to show All involved I could do this. Also 2 weeks later the towers were attacked and now I have many family depending on to support there families. I can say that through my parents and God We made it through. I spoke to my Dad when making decisions. Time does help but I still miss him.