Welcome Riverwatcher,
I have to agree with what NYCkid stated:
Certainly he will be encouraged by congregation members to be cautious with you. Signs you've probably noticed already can include the avoidance of holiday-related functions, birthday celebrations etc. All you can do is keep the line of communication open and be aware that eventually they will try to convert you and your husband as well. If he and his wife do begin avoiding you or state that they need to shun you because of your religious disparities,
Sad to say...being a JW for 19 years, I have seen this situation happen! Hopefully, the bond that you and your husband have with your son, this might not happen. Stay close to your son, Daughter in Law and grandchild as much as you can.
All the best to you
Dee