"are duly working" is a correct and usable phrase in written English.
You can use it to denote that someone(s) is diligently and satisfactorily working on something. Example Sentence: The staff are duly working on the project and should be finished by next week.
The story was duly worked into the serial.
Peekskill residents are duly appreciative.
We are duly capable of successful relationships.
Given these limitations, our conclusions are duly tempered.
The Premiership leaders were duly made to work hard for this win, especially in the first 50 minutes of the match, at which point Ben Foden and Ken Pisi took advantage of loose tackling to put Calum Clark over and give Saints a 15-point lead.
Of course, the girls were duly scolded for turning work time into playtime, but work and play didn't turn out to be all that different.
Glass asked librettist Rudy Wurlitzer to turn the book into an opera and the work was duly sent to Disney Studios for consideration.
Under Stalin, Rodchenko was accused of "formalism", an accusation that beset many avant-garde artists in the 1930s, and his work was duly censored.
This was a poor policy, which was quickly rescinded: "American" was duly entered when editorial work progressed deeper into the letter A, but by then it was too late to make changes in the "af-" section.
All this work was duly airlifted into my production of Iphigenia at Aulis, which played recently at the National Theatre and in which, if you looked closely enough, you might have noticed the constant flutter of the background emotion of anxiety in the chorus, or Achilles's three-metre leap backwards when he is told he is going to get married, or Menelaus's panic attack when Iphigenia arrives.
