Here is a link to fill out MDE yourself.
https://disneyworld.disney.go.com/airport-transportation-reservation/?bhcp=1
It even allows for different members of your party to arrive/depart on different flights. Just be sure to click on "add a person" or something like that. Don't assume your whole party is scheduled just because you entered the first person listed on the reservation. If you later need to make changes, just pay attention to where it asks, "Have you submitted this form in the past for this reservation?" (or something like that) If I'm making changes I just resubmit the form and answer yes to that question. They email you confirmation so you know they got it.
Also when adding children, I prefer to use online chat with Orbitz. I had an awful phone experience where the agent just wanted me to rebook with the kids added and tried to say the price has gone up when, in reality, it was adding their extra charges for 3 or more in a room. Also her English was awful I felt like I was calling some remote village in India or Sri Lanka.
I find the chat agents are fluent in English.
With the chat, I just make sure I do it while Disney has hours and say something like, "In the past, I've stayed on hold while the Orbitz agent calls Disney to verify there's no extra charges." So that seems to solve any issues of them not being sure what to do. Then before "hanging up" with the chat people, I quick log into DME and make sure I can see them. Once they spelled a name wrong and MDE gave me an error like it didn't recognize her. I was glad the chat agent was still there and was still holding with Disney. Got it all straightened out.
When it comes to Disney, there are just sooo many other things I'd rather spend money on than extra $ for the same hotel room.