The Phantom Fires. The Sommerland Chronicles, #1

A doorway in the woods was never meant to be opened. When siblings Emma and Ben Thurston are sent to the isolated Graves Academy, their world shrinks to rules, punishment, and survival. But everything changes the night they discover a hidden doorway deep in the forest-one that leads to another world. A world called Sommerland. Thrust into a land torn apart by civil war, hunted by deadly creatures, and divided between humans and powerful magic users known as D'aille, Emma and Ben are forced to rely on a fierce young warrior named Lara just to stay alive.
But escape won't be easy. As tensions rise and a devastating invasion looms on the horizon, the siblings find themselves caught in a conflict far bigger than they understand-one that could destroy Sommerland completely. And if the doorway between worlds remains open. Earth may be next. To survive, Emma and Ben must choose who to trust, what to fight for, and how much they're willing to sacrifice-before both worlds are lost.