Under the circumstances, your husband and you are fighting an uphill battle.
Because their mother is a JW, it's a sure thing that they are being brainwashed into the JW mindset. The best thing you can do is to try your best to include them in your family activities, to show that you love and care about them. At Christmas time, send them presents, without ever mentioning about the fact that JWs do not celebrate Christmas. Likewise w/ their birthdays. Encourage them to do well in school, to attend college when it's time, etc. Be supportive of what they are doing, while at the same time, stay away from religious discussions.
What will NOT work is this: - directly attacking or ridiculing JW beliefs. If you do so, you are only playing to this cult's teaching, that the "world" is under Satan's control, and that Satan will do anything to discourage them from becoming good JWs.
And if they have access to the Internet, gently mention to them, "there seems to be a lot of interesting websites about JWs, have you checked them out?"
Maybe, as they get older, they will find JW beliefs to be controlling and ridiculous. Be there for them if/when that happens.
Good luck,
/Andy