Sons_of_Durin
For every summer of their lives, Fili and Kili go to their family's beach house and their secluded area of the beach. They're told to always wear their seashell necklaces- even in school, as to not lose them.
Mermaids are a legend, but not like in our world. They are monsters and considered evil, said to snatch children and women from the beach - to drown the children and "breed" with the women. Most believe that they are extinct.
{Durincest in later chapters}