They are twin, teenage, silver-haired, digitalized girls, able to create human-representations of themselves that have mass.
I wonder how they didn't check enough boxes to get more artwork made...

Because its not a mainstream doujin game unlike a certain guy's work or certain people for that matter...

This image appears as back cover of the Astebreed Complete Soundtrack CD: https://vgmdb.net/album/54492
However I still can't find the artist's name; maybe this info will help someone.