They sound to be totally immersed in the JW brainwash. You owe it to your son to cut free of all that is JW.
I agree with whoever said get all the help that is available to single mums where you live. It does sound as if your grandma is on your side. The best thing would be a two-pronged plan to talk with those of your family who are sympathetic, but secondly to rebuild your own life.
Where do you live in the world? If you're in Britain, there is a lot of help out there for young mums, free nursery places if you're working on a low income and help in all sorts of ways. Contact the Citizens' Advice Bureau, and you might also like to contact one of the ecumenically-minded local ministers or priests in your area, because they are familiar with picking up and beginning to heal the damage caused by cults like the Watchtower. You might even find help from a Women's Refuge, because whst the Watchtower does is abuse.