How come the Deucadons never came up for air?

I hope you are not getting tired of them but here is yet another plot hole from Rome's Revolution. Are we really supposed to believe that the Deucadons, some 50,000 strong, hid underground and were attacked just once by the Vuduri and cowered down there?

We'll come back to that but let's consider the absurdity of the Deucadon's situation in the first place. Supposedly they crash-landed on Deucado 500 years before. Because they were never able to recover the cargo compartment, they started their new life on their new world with nothing but the clothes on their back.

Not even one generation later, the inherent conflict between the Whites and the Grays arose and the colonists split into two camps. The Grays were killed when the asteroid (actually a comet) hit the planet and formed Lake Eprehem. The story continues that the Whites took refuge underground.

First: how did they even find the caves which eventually became their homes? Next, how did they see? How did they know to go down nearly a mile underground? How did they excavate and create "Old Town" and later their real home?

I find it kind of hard to believe they pulled that off but it makes the story very exciting. Tomorrow, why didn't they come up for air?