You didn't really ask for suggestions on how to handle this with your husband...but I'll chime in

. If you DO want "open communication," I suggest telling him that you'd like to/are going to "squirrel away" some money for some special surprises for everyone on the trip. And maybe let him know (if you wanted to) some of your ideas of how you're going to save some of the money. Or not. That way you aren't "going behind his back" but you aren't letting him know what the surprise is. My DH would respect that and wouldn't pry - he knows that I like surprises and I like to plan surprises...and I like to find ways to save/be smart with money!
I do have one money-saving suggestion. I don't recall if you said how long your trip would be, but maybe you could do a split stay. So stay only one or two nights at Contemporary and the remainder of your trip at another resort. Or MY dream scenario would be that your Mom can stay with the kids for one night, and you and DH have a romantic one-night's stay at CR!

(But that may not be your dream

)
I wish you lots of success in your saving, whatever you choose to do!