The Staves

The Staves are a British acoustic folk rock trio of sisters from Watford, Hertfordshire, England. The Allmusic journalist, James Christopher Monger, opined that "clear, confident, and classy, the Staves (along with their producers) know that their ability to harmonize (or just sing in perfect, familial unison) is their calling card, and the instrumentation is calibrated according to that knowledge, allowing their vocals to sit fairly high in the mix..."

source: Wikipedia