House of Gods 8: Afterbirth by Samantha Snow

Abandoned by lovers and trapped in their Manhattan apartment with an onslaught of mortals recklessly wielding magic in a witch hunt to destroy them; the immortals find themselves fighting for their lives and questioning the allegiances that they once held dear.
As the dynamics of power on Earth shift, Kemma births the child that was meant to destroy her and her life hangs in the balance.
When only one of them is left with the ability to use magic, it will be a toss-up whether the new child of the prophecy will be the one to save them or destroy them.