I feel your pain. My DH is active duty military too and our last two trips have been R&R between and after deployments and MY WHOLE FAMILY LIVES IN FLORIDA, just not us. So EVERYONE thinks we should "meet for dinner" or whatever. My problem is that once I'm on Disney property, I don't want to leave, I want to park my car and not get in it until we drive home, so I get why you think it's a big deal.
I think you should sent a gift and a card and let them know you're booked, sorry. I don't think that they meant to be malicious or anything, the worse they could be guilty of is a little thoughtlessness. I always tell everyone that if they want to meet up in the parks, we'd be glad too. No one ever wants to pay for a ticket, so they never do. I know it sounds mean, but we get together 4 to 6 times a year and always when we go to them, not the other way around. That's the bad thing about military life. Everyone expects you to visit them, but they don't make the effort to reciprocate.
It's funny, when we lived overseas I heard a lot of wishful "if only you lived closer we could see you all the time!" type sentiments. Now that we live "closer"...well you get the picture.