1/2 mile isn't too long. 1/2 mile (actually, .66 mile) 4x a day in addition to all the walking (yes, we park hop) at Disney is a lot. Like I said in a later post, I think we're going to have her ride with DH on his ECV for the ride to/from (that is, assuming he joins us in the park. Last trip, he only started out with us 1 of the 4 mornings... and left the park earlier than us 3 of the 4 days as well). Dang it! each time I have myself convinced that we don't need a double, I think of something like me being the only one in the park with them, both getting tired and me having to get a tired kid to walk all the way back to the hotel again... I wish DH were healthy; with most dad's there wouldn't even be a question of whether he would be there to help, and there would always be an extra set of shoulders for a tired kid to rest on.
@ *Seanaci* - I have a Jeep Wrangler single stroller. I don't think they make footboards for those, but that would be an interesting option - save DD6 some of the steps to/from the hotel, while still not giving her the comfort of a regular stroller.
HUGS for you. No one can judge until they have been in your situation. Prayers that your DH has a healthy trip and your little ones have lots of walking energy and you get the rest you need!