I'm so sorry to hear that you are going through this.
Another poster suggested contacting the authorities with your concerns about this being a sham marriage. The appropriate agency to call is ICE.
Other than that, there isn't much more you can do. You expressed your concerns to your son and he didn't take your advice. At least you tried---that's the important part.
ICE tends to take green card fraud seriously. Plus stories abound about men marrying a foreign woman who is only in it for the green card. These women, at some point, try to provoke the husband into assaulting them so that they can make the claim of being in an abusive marriage.
I wish you the best when it comes to dealing with this.