Maddie,
its been a while since you and I conversed. I really sorry that this is hurting you so much, and I fully understand that you must love your family so much. A new baby does bring such joy and should bring much love into a family.
I'm afraid I havent really got much more to offer than that which other board members have already posted, and they are all valid ways of trying to deal with the situation.
I know its not quite the same... I'm not yet a grandmother, but I did have a similar situation, in that I used to spend an awfull lot of time with my young nephew. Oh Maddie, I love that little lad so much, and I miss him.
However, and I don't know if this is going to be of any help to you, I have to sort of put my feelings and thoughts of him to one side because I cannot change what is happening..... I know the JW drill! It will never change the fact that I love him, but I know what they (my family members) will do in dealing with my exit from the borg.
My thoughts are with you; I think what your son is doing is mean and nasty, and you don't deserve to be treated like this, but sadly, by experience I have to concede that this is what they'll do. Fair play to you if you can get them to act differently.
Kindest regards. Shell69