J-DUBBED,
There's a lot of great advice on this thread.
i just want to emphasize the importance in focussing on rebuilding the relationship with your son and his family outside of the religion. If you want to be successful, it must be unconditional (accepting and respecting his wife). I know this is not easy when they allow the religion to dictate their relationship with you.
Be a source of relief for your son. Try to build trust. This way, overtime, he may have you and your wife to confide in when things are not going well with the religion and/or his wife.
At the same time, start planting seeds (without directly criticizing) like someone else mentioned above. Bring up a question, say someone else asked you or maybe in a matter of fact way (give time to think, but don't expect an answer). Don't argue the answer, the goal is to help them think for themself. This also enables him to think about it with forcing him to defend the religion to you.
I was raised catholic. My mother was confrontational and critical of JWs from the beginning. This pushed me further into the religion. I did the same as your boy, referred to scriptures to explain everything. I dearly hoped my mom would convert but isolated from her because I felt her as a threat. I thought I was doing the right thing for my family It took me 20 years to open my eyes.
I hope your son comes out sooner. If so, he will really need you guys support. Don't come off a threat, be a source of comfort. Continue to work on your relationship now. It will not be easy for him to just walk away, so he will need your support.
If you haven't started yet, read the books mentioned. Keep posting and asking questions.