Dear B
I agree 100% that your husband ‘should’ clear your name with your in-laws but an ultimatum that he has ‘got’ to do it by a certain date concerns me.   What if he doesn’t?  It seems to me to be a tremendous pressure on someone so early in recovery.
Your husband’s behaviour ‘should’ give his parents the knowledge that you want passed on to them.   If it was me (and this is only my opinion) I would give him time and watch for their behaviour to change towards you.   If it doesn’t then I would think your husband has a duty, towards his wife, to talk to his parents but I am concerned he will not have your strength yet.  I hope it is something he can raise with them but I am wary of an ultimatum to do so.
One of the things I have learned in my recovery is that it is possible to regret speech but never silence.   There have been a couple of issues (not related to my CG but as a result of the addiction in our family life) that have left me seriously distressed.  In my pre-recovery I would have launched in because I don’t like lose ends.   I still don’t like lose ends but with the benefit of hindsight I am finding that those who have distressed me have changed more because of my silence than my speech.  In one instance there has been no closure but the person who caused the distress is working overtime trying to please without giving it, which is harder for them I think.
I’m not sure how he intends to work the 12 steps with you.   I have done them and I believe they work in a separate recovery – his with GA yours with non-CGs.   I think it would be a one-way traffic from your husband and I am sure that is not right for you.
The Gamanon 12 steps is the same apart from the 1st step which is altered to    
1          We admitted we were powerless over the problem in our family.
To admit our powerlessness over the problems we face gives us a wonderful feeling of release.  We learn we are not responsible for the gambler’s problem.  We cannot stop the gambling, no matter how we try.  We also learned we are not to blame for the gambling.  With this understanding of our powerlessness, we begin to feel free to concentrate on our own problems.
I know that many non-CGs in my group (including me) struggled with different steps.  It was only within a group of like-minded souls that I accepted many of them –one in particular.   I remember a lot of emotions that came up in my group that were best left within the group but we did always manage to come to a calm understanding before we went home.   I think I would be inclined to suggest he works his 12 steps with his sponsor and perhaps remind him that you have to work your recovery too. 
Counsellors have the ability to open a person up and close them again.    My feeling is that loved ones can open each other up far easier than they can find closure.   
I hope to speak to you in a group soon.  I also hope I am making some sort of sense.   I know you will come back if I am not.