I have not heard of any historical basis for the complete sweeping of the Household Staff as depicted in the movie.

The man who found Stalin was Peter Lozgachev who was not summarily executed and in fact lived till the fall of the Soviet Union and gave interviews in the 1990s. This would be the first clue that the household was not simply executed wholesale as depicted. The other would be that Stalin's housekeeper, Valentina Isomina was also alive and well and did not die until 1995. Both of these facts point that it was unlikely that the household staff was "liquidated" as portrayed in the movie.

I have watched the movie and I do actually really like it, to be quite honest. Jason Isaac's portrayal of Georgy Zhukov would make /u/Georgy_K_Zhukov proud. The movie however is not a completely accurate portrayal of events. The Beria execution was months later, for example. The scene showing the complete liquidation of the Dacha was likely a way to show the ruthlessness and way that the NKVD under Laventiy Beria was used. That simply being connected to an event or connected to another person who was connected to an event could lead you to be tossed away or sentenced to death.

The issue is, that the way about they conducted the executions of the household staff runs counter to how often the NKVD operated. In the scene before they kill the staff, Beria is stealing the death warrant lists of political "criminals." This highlights the bureaucratic nature of the NKVD and the Soviet Union. Executions had to be stamped and signed, not simply a hack job in the dark of night. Even during the height of the Great Purge there was "court" decisions on the outcome of prisoners and criminals. Even if the court decision was already decided and the facts of the case may have been fabricated, there was a veneer of justice slathered over tyranny.

The execution of the staff ties also into an idea that has been floated around since Stalin's death about the timeliness of his Death and the events around his death. There is theory that Stalin was poisoned by Beria or someone else in his court and the liquidation of the staff at his Dacha would tie up the loose ends of the conspiracy. This idea is toyed around with in the movie, although not really being completely explicit. The follow-up theory that is presented heavily is that Beria especially slow-walked any attempt to aid the unconscious Stalin. Killing the staff would be a way to cover-up the slow-walking and other acts Beria committed while being the first to arrive at the scene.

So, in a way the movie makers decided to portray the death of the household staff of Stalin in a way to show the ruthlessness and villainous nature of Beria quickly. They also did this to tie up some plot-holes if they arose. This however runs counter to how the NKVD normally operated (with confessions and trials before any executions). While also a couple of big name household staff lived until after the collapse of the Soviet Union in 1991.