A: Zeus is not among the Gods of Arcadia. He caused much of the strife and unrest among the Olympians on Earth. Hestia insisted he could not be part of the new Utopia.
A: In Earth time the exodus from Earth is still at least a century in our future. The Olympians are still meddling behind the scenes. I assume the trip to Arcadia takes some time, then they have been living on Arcadia for 2000 years. It is the far future.
A: Most of the images of the gods and goddesses, including the covers, are made by Howard David Johnson and used with permission.
The remaining images of the gods and goddesses are in the public domain and largley come from famous works of art. If you decide to check these out, bear in mind that some of the full images include artistic nudity, a common feature in this genera of art.
There are a few exceptions to this trend, including the art of the crystal for the crystal reader, the image used for the Gaea stones, the book wallpaper, the Olympics symbol and, of course, the Disney logo.