Coming from a step family myself, I can't stress how important it is to your children that the discipline comes from you - NOT the step dad. He can be in on things, but you are their natural parent, and I think they would accept things better coming from you and not him, resentment will creep in if he does all the discipline. This might seem to go against the whole "head of the household" theory but I can't stress how important this is.
Another thing, instead of saying this comes from the "society", "org", "elders" or "KH" maybe suggest to your husband to show the children from the bible and the bible only, no JW publications. You and your husband can sit down together, before hand whenever possible and discuss your course of action. My father did this, sent us to our rooms, prayed about the situation, and showed us from the bible whenever possible why we did what was wrong. (He came from a very abusive father, and never, ever disciplined us when he was angry - he took some time to cool down first by sending us to our rooms.)
He knew your views when he married you, he has to respect your views as well, and recognize the fact that they are YOUR children. It is a two way street. When your child together comes around, I think you will have to lay down some ground rules right away.
BB