The problem you have is if your husband has doubts but still believes he may be sucked back in. JWs are very effective at applying guilt and pressure to get ex believers back in line and unless someone is mentally free they are still influenced by all this. The other thing is when JWs are processing difficult situations they can shut out the unbelieving spouse since JWs are conditioned that this is a personal struggle and not to be influenced by worldly influences they will see you as part of the problem not part of the solution. Be aware of this and if your husband starts to withdraw from you you might get an early heads up that they are affecting him more.
I would avoid confrontation but I would suggest being polite but firm. If they try to pressure you to study or look more into their faith then thank them for their offer but say that you are happy with your faith and have no wish to study with them. If this should change you know where they are and would come to them.
Be curious and question every assumption. Talk to your husband about what was said get him to think about things that he has accepted. Not as a challenge but as someone who would like to know the answer. Getting him to look into things and explain will help him understand why he has doubts and clarify his own concerns.
Good luck