Rebel Fae by Ingrid Seymour

The island killed my friends, but I survived. Now they’re forcing me to go back.
A month ago, Adaline and Alexander Habermann ripped me from my home and the people I care about, but that seems a lifetime ago. The twisted twins run a sinister experimental facility disguised as a rehabilitation island.a
They brought me here along with other Supernaturals who became my friends and fought with me for survival, but now they’re gone, and I’m still here, a prisoner.
But there is a new twist. The twins say I can earn my freedom, but only if I help them. They want me back on the island to guide their fresh recruits—a terrible combination of vulnerable, young wizards, and blood-thirsty vamps.
What happened last time still haunts me, and I can’t trust the twins’ promises. But what choice do I have? I must comply or stay a prisoner. Or worse, become a victim of one of their cruel experiments.
To make matters worse, I have to work with Vaughn—the same werewolf I thought I had feelings for until he savagely betrayed me. We must figure out a way to keep these kids alive while the island does its best to kill us all. But Vaughn is dangerous, a vicious werewolf who only cares about himself.
What will kill me first? The evil twins? Their island? Or Vaughn?