Left to right: Io, Europa, Ganymede, Callisto

Io, Europa, Ganymede, and Callisto are the four children of Zeus. The eldest is the only male, Ganymede, whilst the other three are female.

As Zeus was the first of the elemental nevreans to settle down, these four are the eldest of the moons (besides Selene); only one other, Titan (one of Saturn's sons), is slightly younger than Ganymede. Zeus loves and cares for all four equally.

Io has had persistent digestive issues ever since she hatched, and thus belches and passes gas often, much more than normal - much to Europa's chagrin. She is thus reserved and shy about her condition.

Europa is the youngest, and is a reckless prankster who loves to mess around with her siblings with all sorts of antics, but also has a love for tinkering with gadgets like Gaea. This has caused her to get into trouble quite a bit.

Ganymede is the eldest and the only male of the four, and is a protective, rule-abiding role model for his younger siblings, though he is willing to let loose sometimes.

Callisto is the second eldest and she is self-conscious, shy, quiet, and reserved, mostly due to her little sister Europa and her schoolmates constantly teasing her.

Io, Europa, and Ganymede have a special connection to each other and to their father Zeus, where they can synchronise their actions almost as if they were reading each other's minds. This, however, has been used by Europa to play pranks on the others, most often Callisto, and often to the chagrin of others.

Nevrean species by  Mick39

BTW I am NOT gonna make all 97 moons of Jupiter!