The River Has Roots by Amal El-Mohtar

In the small town of Thistleford, on the edge of Faerie, dwells the mysterious Hawthorn family. There, they tend and harvest the enchanted willows and honour an ancient compact to sing to them in thanks for their magic. None more devotedly than the family's latest daughters, Esther and Ysabel, who cherish each other as much as they cherish the ancient trees. But when Esther rejects a forceful suitor in favour of a lover from the land of Faerie, not only the sisters' bond but also their lives will be at risk.