Photo by Johny Li on Ami Harikoshi's photostream.
I was having a tough time finding a photo of some sisters on istock and the like but then I found this on flickr. It is in low light, so the pixel quality is not that great but the expressions are very sisterly. Only trouble is, one sister posted the photo to her photo stream, so does the other sister mind? I hope not.
Unbound licence (free to use as a photocopiable resource but not in a book). Do not use the model for anything other than this resource.