There is no park transportation from DTD. They would have to take a bus to a resort, then take a bus to the parks.
Each park has a guest drop off area. Go directly to the right most booth of the park you are at and let the CM at the gate know that you are dropping off guests. They will direct you to the guest drop off area.
Another option would be to drop them off at one of the monorail resorts. As I’m sure you know, its a short walk from the Poly to the TTC where than can take Disney Trans to any park.