The Power of Averborn. Bounders, #3

Sixteen years of torment. One dragon's desperate gamble. And twins whose fate was sealed before they could even speak. Harpur Diggins has been bound in chains of flesh and magic, his spirit trapped within the body of Karrys Evergreen and subjected to unspeakable torture. At last the prison begins to crack-but freedom carries its own peril. To escape Karrys is to confront the weight of his past: his mistakes, his betrayals, and a forbidden sigil burned into the foreheads of two innocent children.
Meg and Hart were never meant to carry dragonfire in their veins. Yet Harpur's desperate act long ago has awakened a terrible inheritance-one that threatens to consume them even as it offers the only hope of survival. For in the frozen heart of Averborn, the twins will rise as Ice Dragons, their bond reshaping the destiny of kingdoms. The final battle draws near. Old enemies tighten their grip, prophecies unravel, and sacrifices demand to be made.
To save Epoh-and himself-Harpur must face the fire and frost he unleashed, and the children who will bear its power long after his own flame has burned away. The Power of Averborn is the searing conclusion to the Bounders of Epoh trilogy: a tale of captivity and freedom, guilt and redemption, and the kind of love that survives even dragonfire.