Welcome Single Dad
It sounds to me like you are a great dad. First of all, you have so many positive things to say about your son. You are obviously giving him the praise and encouragement he needs to become a fine young man.
I do not think you have too much to worry about. I would be sure to let him know that he can make up his own mind, and that you have confidence in him. However, you might, to help him decide, look up some info about the history of Jehovah's Witnesses, starting with their founder, Charles T. Russell. Progress to the next President, Rutherford. They both made some pretty bizarre predictions and statements. Back in the early J.W. history, they said that vaccinations were "like taking puss into the body" and other ridiculous health statements. You could show him the false prophesies made by these men. He could even share the information with his mother and ask her about it.
I feel bad that your son is being torn and made to feel guilty. Above all, the WT Society heaps this on its members. Wouldn't it be better for his mother to also show her pride in her son instead of constantly telling him God doesn't like what he does?
Please, at all costs, try to discourage your son from being baptised. Then if he makes a mistake, sometimes even a minor one, he could be treated terribly by this organization. You have only to look at posts from this site about disfellowshipping and shunning to see what it can do to people.
Keep up your good work as single dad.