A lot of good advice in this thread. I wish you both the best. As I see it, ultimately, the marriage at its core after that day is between you two, no matter how big a role family plays or doesn't play in the future. Given that, if I were you, I'd try to make it easy on you both, and to communicate with each other about how best to support each other to get through it. I do think the wedding as pageant is about family and community (or actually about who pays for it -- which is ultimately a gift, and I feel like I can't dictate or question gifts, just thank the giver).
Maybe taking your own personal vows ahead of time, or maybe planning a special moment at the honeymoon feels right -- I just feel like keeping it simple, private, and not entailing deception or extra planning might be compassionate as so much is on your plate. Maybe you can hire a photographer you like to take a few shots ahead of time of just you two, or maybe you can do this on your honeymoon.
My biggest question is when will your husband move out of his folks house? Can he stay at a friend's house or elsewhere briefly if it helps reduce the stress levels? Do you have a plan for living together and being able to build your own bond after marriage?
In terms of communication about the wedding itself -- invitations and such, I feel like all weddings have moment of miscommunication and frustration (lol mine did and there were about 10 people there). Most of the people at the wedding you will never see again, so you really don't need to worry about them and what they might or might not know or think, just smile and accept congratulations. In terms of the secrecy regarding your family. Will your family be there? Will they be made comfortable and welcome by your immediate in-laws? That's the most important part as I see it -- not what issues a second cousin might have.
I echo that ultimately it's just a day, and very likely not one of the most significant or meaningful days of your marriage (I really liked my wedding and I've been married almost 20 years, and it's definitely not anywhere near the most meaningful or romantic moment.)
ETA: Janet, I feel like 'the couple's day' is what most everyone expects in the US, but in reality parent's (especially mothers) can have very specific ideas about how to best celebrate (their vision) of the couple, and can believe they know best, more than the bride many times, about how to do that.
My sisters wedding involved a culture clash between her Latin and South American friends and co-workers (and her) who thought weddings were for lots of dancing and music and laughter, and her husband's somewhat strict northern European religious family, who thought weddings were for quiet conversation and a very long kneeling ceremony. The compromise was a bit disjointed and the MIL closed down the reception at about 9 pm just when the party was getting going. She totally meant well too