It seems to me that in your case, this child is distraught over the divorce of his parents ande totaly jelous in you and your kids. Some times children feel that when thier parents split up and one maries another person, that hte prarnt who got remarries loves his "new" family now and not them. Sorry to confuse you. To make it sort of easier: This child might be showing hatred because he is jelous of you and your children because he feels that his dad left him and his mom for you and your children.
The best thing to do is see if he wants to talk to your or your husband. He might feel uncomfortable which is totaly normal. However there are other forms of talking like aprogram at school for children going through divorce and ther oare formes of therapy and counseling (one on one, Group, and family).
It is hard being in your position because I am sure you and your kids mean no harm to him or his family. Things like this happen alot in familys. If he does not want to cooperate with you and your husband at all, The best thing to do is just keep your kids out of his influence and just let your husband do things with him. He just wants to get the attention from his dad to show him he cares.

I hope everything works out for you. I am sure it will.
Good Luck.

Roman James