Crystal Bones (The Faelin Chronicles)

The first book in a trilogy that features a twin sister and brother who are half-Fae and half-human. When they discover their younger sister is missing, their home burned, and their parents murdered, they seek revenge on their goblin enermies.. Their father’s last words lead them to Eirian, a powerful sword that will take them to their missing sister, if they can keep it out of the hands of their enemies.