Frankly I think your kids..especially the 2 year old...are way too young to enjoy or even REMEMBER a trip to Disney, 6 months from their visit.
MS certainly is unpredictable. But it's not terminal. And there are many many folks who don't have serious disability from it, and rock on for YEARS without anything really major going on. Perhaps you'll be one of them. 2-3 years from now..when the kids are older, you are back to work, your finances are in better shape...Disney will still be there. And it's quite likely you'll be able to go. Maybe you'll need to rent one of the scooters they have available, especially if you go in summer, when it's way hot...or maybe not.
Of course the bigger issue isn't your trips to Disney..it's your sens of impending doom. It's "more impending" for us who have a chronic illness, to be sure...but truth is, life is unpredictable. People get injured...even killed...all the time, and before they've done all they've wanted to do in life! You can't rush experiences, can't rush "living" into your kids. You can just do it with them, day by day.
I think it's fine to focus on every single moment. But you can't begin to pack a lifetime into any one day. All you can do is do the best you can that day, go to bed, wake up in the morning, and do the best you can with THAT day. And pretty soon life will rock on, and you'll be in it -- maybe not in the same way you were before MS -- but you'll be there, playing with your kids, sending them off to high school, dancing at their weddings.
I've had MS for 24 years. Since having MS I've travelled to Canada several times, all throughout the US, to the Philippines in a wheelchair!, to Alaska... This summer I am travelling..by myself..in my wheelchair..by Amtrak train..to Portland, Oregon, half-way across the country from where I live. Do I wish I could do it without the chair? Well of course. But I can't...so I do what I have to do to enjoy my life. So will you.
What do you do for a living? Is there a way that, with adaptations, you can get back to work, if that's what you want to do (and your family needs the $$)?
...I am not a doctor, nor health professional, and don't pretend to be one, here.....