Sapphire Falls by Audrey Lynn

Trapped in a realm beyond their own, two sisters must face their destinies…

With the Latian King dead, Avery Hollis thought she was safe from danger and could finally bond with her soulmate, Savine Ralathian. Now, with her sister Morgan in Aeritis—the land of the Fae—kings are vying for control of the prophesied twin witches who could transform the realm. When King Rylo demands Morgan for himself, Avery is forced to choose: protect her sister in the treacherous fae realm and stay with her soulmate’s sworn enemy, or join Savine in his newly unified nation.
But nothing in Aeritis is that simple. When the Goddess Althea commands the sisters to search for five ancient relics, Avery and Morgan are thrust into a dangerous quest, where they are not the only ones seeking the hidden powers of the relics.
As Morgan’s powers spiral beyond her control and Avery’s bond with Savine deepens, the sisters must decide: will they stand united against the forces that threaten to tear them apart, or will they find themselves divided by the political divides of a perilous land?