Ranobe No Hen!

Sugano Ikkei is a typical teenager at his high school and lives with his older brother Hyakkei who is an editor at a publishing company. Hyakkei is in charge of several artists and writers and his job is to support them in anyway possible. However, he broke his leg and is unable to leave the hospital for a week and he has a very important meeting with a very shy writer named Tokito Aona which has taken months to get a face to face meeting.
As they look really alike, he asks Ikkei to dress up as him and go as Hyakkei. The meeting goes well without her knowing the truth, but Ikkei is forced to go to another meeting with Fujimaki Misuzu, an artist moving to Tokyo in order to continue working. To his surprise, both girls, Tokito and Fujimaki, are in the same class as he. Now he has to juggle being Hyakkei as an editor to the two girls as well as be their classmates as Ikkei, and do all this without letting out the secret that he is the same person.
(Source: MangaHelpers)