Perez Hilton turned me on to their gorgeous cover of Britney Spears' "Toxic" and I totally dig the two other songs of theirs I've heard, including another great cover, this time of The Cure's "Don't Love You". You can check them out
here.
As far as I know they don't even have a CD out, just a hard to get EP, but they've been singing together ever since they were wee sprogs on car trips with daddy (folk singer Tom Chapin, Harry's brother).