Kingdom of Sirens and Monsters. Kingdom of Sirens and Monsters, #1

"Mirror, mirror, in the shell that thy lay, Who is the fairest in Odyssey Bay?"On the island of Odyssey Bay, a wedding day looms-and Coral will do anything to stop it. Since their mother died, twin sisters Coral and Kendra were raised solely by their father. But since Melody came along, their father has been swept into a blinding, whirlwind romance that Coral fears will end in heartbreak and loss.
It feels like nobody but Coral can see Melody's true nature-she's wretched, power hungry, controlling, and clearly desires to obtain their island resort and family wealth. But Kendra adores Melody, and her father is smitten, leaving Coral the sole sceptic. Then Coral meets Lysander-a mysterious, handsome stranger who returns her surfboard after it's lost in a storm. Lysander knows things about Melody, about Coral's dead best friend Maya, and about Coral's mother.
When Melody's true and terrifying nature is revealed, Coral has no choice but to escape to an unknown world beneath the sea-where ancient magic, family secrets, and power she didn't know she possessed awaits... A Snow White meets The Little Mermaid retelling