According to a flyer I got before I entered the parking garage, Grinchmas is from November 23 to December 31.
The ride on the railway in Seuss Landing is the Sneetches ride. It may never open due to issues with the ride, load times, etc.
As for Pternandon Flyers, they only let you ride with a kid because when the ride first opened, everyone rode it. It was supposed to be a ride for kids, but adults hopped on too. The ride has the lowest capacity in the park, so a one minute ride had around a 45-60 minute wait. Now with the restriction, wait times are about 50% less.