A demigod in the lost cities

Ellie Searle and her twin brother Jacob find out that they are half-elf as well as demigod children of Poseidon. their mother is Vivian Vacker who fled the lost cities. now they go to the lost cities and meet their cousins Fitz and Biana and the famous Sophie Foster.

takes place after HoO (heroes of Olympus) and during lodestar
everything and everyone except for my characters belong to J.K. Rowling and Rick Riordan

I don't recommend unless you have read Percy Jackson and / or keepers of the lost cities