Thanks to Trevor Brown's blog I spent the last hour watching Youtube videos of these fabulous creatures. (This particular video was posted on Youtube by Archpope.) Their website says:
"New classical music spun out by two twin young girl dolls for the first time in Japan! At the center of this charming Kokusyoku Sumire (Black Violet) are Yuka, the genuine soprano songstress with the attraction of a little devil, and Sachi, the exceptional violinist and model who strikes adorable poses. The girls express with extravagant freedom motifs based on internationally known fairy tales such as the “Little Red Riding Hood”, “The Little Match Girl”, or “Hansel and Gretel”, while adopting a diversity of elements from such music genres as chansons or classical music."
Have a look at their website: