HeyThere, as I was reading your post I thought of the experience provided in this thread by Don Cameron, author of Captives of a Concept - highly recommended reading for you.
Sounds like you're very fortunate in that your husband and in-laws don't appear to be hard-core against what you are saying, taking more of a Christian-esque approach to your difference in understanding. Use that card wisely. It is unique. May I suggest you get Don's book and try the method used by the guy in this experience.
And best wishes on your surgery.