The one to the right is her senpai, the one to the left is their boss on a cafe. This illustration is from an ero-voice doujin work (seems I can't post the link, but you can find the link to the work in the source's description).
According to the artist's twitter, it's a promotional image for a DLsite erotic audio file. The premise is that the listener is working a part-time job at a bookstore and gets magically transformed into the main character of a yuri novel, causing your senpai and boss to relive the events of the novel by, well, tying you up and doing lewd things to you.
Yeah, it seems like there wasn't very much yuri fanart of Yuel and Socie until the new version of Yuel with the very gay art was released, at which point there was suddenly a whole lot of it.
The source confirms that this is, in fact, yuri. The girl on the right's just a tomboy.
Also! This was made by Yuhuko Suzuki, who wrote Candy several years ago now. I'm happy to see more from her, and even happier to see that she's still doing yuri now.