Book ID

[Yanni Cooper]

Someone asked me if I knew this book, and it rings a bell, but I can't
for the life of me recall the author or title.

It's about 7 brothers who are turned into swans, and their sister frees
them by weaving them shirts of thorns. However this isn't the original
fairytale but rather a fantasy story based upon the fairytale. Any help
would be greatly appreciated.