The world of Myr is in orbit around binary suns.
These solar twins provided the basis for all mythology and culture of the people of the archipelago. Everything is defined by duality (shorthand: Yin and Yang).
There is a God and Goddess who each have two forms each with twin children. These four children each have split personalities that become stronger and weaker with the waxing and waning of the four moons.
On a water-world like Myr, two of the moons are close enough and positioned in a way that replicates the effects of our own moon. The other two are so small and far away that they have little, if any effect.
The two closest moons are made of a much brighter rock than ours (Earth’s moon is actually very dark and reflects only about 10% of light that hits it). So moonlit nights on Myr are much brighter than ours.