It can all be done on one form. Each person on the reservation gets their own section.
OR
You can fill out multiple forms, listing only the people you want on that form, but all forms referencing the same confirmation number
OR
IMO, the best way to do it is to call DME directly at 866 599-0951. This is not a Disney phone number. The wait will probably be 0-2 minutes. Just tell them what you want and they'll set it all up for you. It's quick and painless.
Steve