So, I took Bumpershoot's suggestion and called my brother. He is the sweetest guy! He thanked me and mentioned that he knew I would make a way for his kids to go if he wanted me to.
He feels torn, as expected. He's afraid that his wife will insist that all three kids go at once which, my husband and my mother both think is too much. They're not being mean, just realistic. You would have to spend a day with the kids to understand.
My brother and I are going to make a plan together so that after a couple of years when his immediate bills are under control, he can start saving a bit from his second job. I will save air miles (I have a business and accumulate miles pretty quickly) so that I can pay for airfair for all 5 of them. We will ask for my parents to consider paying for an extra hotel room, I'll pitch in some for park tickets and we should be able to make it work.
It will take just over 3 years or so but the kids will be around 12, 11 and 9 and will be a great age to remember it forever.
Plus, I get to look forward to going to Disney with my brother! Whoo Hoo!
Boy do I appreciate everyone's input. I just needed to get a feel for someone else's take on the situation so that I could calm down a bit and think rationally!