When citizens of the planet are shown, the children are depicted as twins.
This follows the comics, in which Lightning Lad's home planet has an usually high number of twins, to the point that almost everyone is born as twins; example being Lightning Lad's twin sister, who is also in the Legion (Lightning Lass).
On the other hand, his older brother Lightning Lord was born as a non-twin. Which is a nod to him feeling of resentment due to being different from the rest of society, and a reason to why he is evil...or at least not as heroic as Lightning Lad.
On the other hand, his older brother Lightning Lord was born as a non-twin. Which is a nod to him feeling of resentment due to being different from the rest of society, and a reason to why he is evil...or at least not as heroic as Lightning Lad.