I'm assuming that reservations have already been made for them to use DME, correct? If not, call and make them their reservations. They will have all the info they need in the info packet that gets sent out a month or so before they are due to fly. In that packet will be directions to the DME checkin counter, their yellow luggage tags (which will go on any checked bags), and their vouchers. When they get to the DME checkin counter, they will hand over the vouchers, which will be stamped. They will be directed to the correct bus line for their particular resort. When they get to the bus, their vouchers will be scanned and on the bus they'll get.
They will only need their vouchers from the info packet...no other ID will be needed, at least it hasn't been the three times I've checked in.