A year after the marriage of Queen Celestia and Queen Novo, they decided to have a foal together, mostly because Skystar was traveling Equestria and little Equius would love someone to play with closer to his age (Celestia, Novo and Luna had royal duties after all). The thing is that Novo thought they would have one egg, like in her pregnancy with Skystar, but noupe, they had quadruplets. Equius was thrilled with the little balls of feathers that were her sisters, and loved to held them. Skystar loved her little sisters, and was delighted to see her two mothers happy.
 
From top to bottom:  
Princess Astraea Radiance of Equestria, she is kind of stern and firm, like Novo, but deeply cares about the people she loves and her kingdoms, she is responsible of the justice in the lands.
 
Princess Ondina Gleam of Equestria, she is calm and realistic, she seeks knowledge. Loves to spend her days writing.
 
Princess Marina Glister of Equestria, has a bubbly personality, but isn’t afraid of showing a more mature one, she tries to keep the people of her kingdom united and happy. She is the most seen in Seaquestria.
 
Princess Amalthea Light of Equestria, she is captivating and knows how to manipulate things in her favour, she isn’t just a pretty face.
 
About their appearance: Their hair represents the different looks at the sea through the days: Sunrise, early morning, midday and sunset. They have magic, but since none of them have a horn, the gems in their crowns catalyze their magic.