This is going to sound harsh, but your kids are just being ungrateful brats! I badly wanted to go to WDW since being a little kid, and finally got to go when I was 14. At the end of the day, whether they like disney or not, a vacation is a vacation, and they should make the most of the opportunity that many kids don't get. Also, I don't see why staying home for social activities is important, why should you lose all that money just so they can stay home and play sports and do all the stuff they do every day anyway?
Make them go, don't let them get away with their behaviour. And another thing, be careful they don't try to act like martyrs about the whole situation, as though they're making a huge sacrifice for your sake, make sure that they realise that the vacation is as much for them as it is for you.
I know what it's like to love something and plan something and then have family trample all over it without a care for your feelings, but don't let it happen. If they're sick of hearing you talk about disney, tell them that you're discussing a personal interest, just as I'm sure you're expected to listen to them talk about their "social activities" all the time. They need to realise that this trip is important to you, and you need to make sure they know that.
OK - I know it sounded a little harsh, but I'm sick of reading the "sit down and hug each other" replies to this thread.