I remember a scene where they fly over a wall and land in a forest.
They find a huge home and realise that when the world was dying due to overpopulation, the poor were moved to the walled area while rich elites got to enjoy a green world.
There was also a scene with an animal who didn't attack them due to something in the DNA, which I think meant that the walled humans also were genetically spliced with animals.
This sounds like either The Roar or its sequel, The Whisper. Here is part of a summary of The Whisper: After discovering that the world was not covered by catastrophic plague or poisonous yellow dust, telepathic twins Mika and Ellie realized that the government lied to the population. The governing elite wanted the people to believe this so that the rich could live in luxury on the southern side of the Wall while the most of the rest of the people starved in cramped conditions in the north. I also recall that one of the characters (I think in The Roar) unfurled their wings, and that the main character had webbed feet.
