You've been watching Philadelphia.
Its simple. Have they received their luggage tags yet? If so, just have your parents attach them to the luggage they are checking in at the airport. Make sure they have a carryon with items they need as soon as they get to the hotel. They will not get their luggage for at least 3 hours.
When they get off the plane, they will take the monorail to the main terminal. I am not sure where the ME desk is located but there will be Disney Cast Members in the airport with the big Mickey hands. Make sure they have their reservation # on hand so they can check in. After check in, they will direct them to the correct line to get on and then just wait for their bus to arrive. That simple.