A few years ago I listened to a documentary on the radio about sibling harmony - the singing sort though, not the sort illustrated by two brothers restraining themselves from punching each other. It looked at how the combined vocals of siblings produced a much more natural and almost inseparable harmony than that produced by any other group of singers, no matter how good their individual voices. One of the main reasons for this is because siblings share so many physical features, such as the shape of their noses or the colour of their eyes, and so it stands to reason that their voices will be similar too. Add to that the fact that these voices resonate within physically similar chambers in the mouth and nose which amplify and colour the tones, so that the singing of brothers and sisters is of a similar timbre. That's nature taken care of, but "nurture" factors such as accent and vocal intonations will also play their role in ensuring that when family members sing together their voices blend together as one. Just think about the number of famous singing family groups since the 1940s. And then add the Staveley-Taylor sisters to your list, better known as The Staves.
A few summers ago I had the pleasure of photographing The Staves at an acoustic gig on a beach here in Cornwall, organised by my oldest friend Alex. He recently worked with the singing sisters again to produce a couple of Take Away Shows with French music videography pioneers La Blogothèque, and the results are wonderful. Take a listen, and a look too.