Storm Hawks/WMG

Lightning Strike is Aerrow's late father.
Bam. Might as well start with the obvious.
 * One wonders why they even say "ancestor", and not "father", considering Lightning Strike died in what looks like his twenties when Aerrow was about four. Even more perplexing, when Aerrow finds out about the relationship, his only reaction is, "cool!" Wouldn't finding out one's long-lost father was a Storm Hawk elicit a more excited reaction? Then again, he did end up following his father ancestor's footsteps, so...
 * He could also have been a Disappeared Dad, considering Aerrow didn't know he was his father ancestor. Not only that, if LS was a celebrity, and the Storm Hawks had something like groupies...

Atmosians have a much larger lung capacity than most earth-dwelling humans.
Picking up oxygen in high altitudes and shouting to each other over loud engines made this trait much more favorable.

Atmos has lower gravity than Earth.
Leave aside all the issues regarding unlikely levitation and whatnot, most of the Atmosian's body types seem to trend toward lithe and lanky, but with proportionally large upper torsos. These resemble some scientific conjectures about what a humanoid species on a lower gravity planet may look like. Plus, y'know, all those crazy aerial stunts they pull would be helped by lower gravity.

The Leapers are in fact members of Ridley's race, in their juvenile stage of development
This is mostly a joke, but they do look like a variant species of little Birdie. Possibly a group the emigrated to a different planet, and adapted different features.

Radarr is actually a child Blizzarian
Apart from tail length and the ability to talk, there is remarkable similarity between the Blizzarians and Radarr.
 * Alternatively, Radarr's species came from Terra Blizzar.