I wouldn't worry about it too much. The past few years my parents have driven down in the RV, and I fly down to meet them, taking the DME to the Fort. Most of my stuff is pre-packed in the RV, and I just bring a carry on.
I've had a year where my DME info was wrong, and another year my DME package never arrived. I'm leaving next week, and I haven't recieved my DME package again this year.
Each time it hasn't been at issue at the airport. Just make sure the folks flying in have your WDW resort confirmation #, and that thier names are on the reservation. The flight times can be wrong, and you don't need any paperwork ... they can check your confirmation # and names at the DME desk, and they'll get them on a bus. I've been through it before twice, and never had any issue or delay with the DME folks.
Just double check that thier names are on the ressie and they have the resort confirmation # to present at Orlando airport
EDIT: Just wanted to add that the one year my flight # was correct on the website, but the flight time was wrong ... again wasn't a problem at all getting on a DME bus when I arrived