This is an old topic, the inaccuracies, etc, in "The Lost Prince"... but having seen this movie a couple of times, I think I may have some insight. First of all, remember that the movie is portrayed from, largely, the perspective of the British royal family. When King George receives news from Russia it was probably sketchy, at best. Being told, for example, via reports from the F.O. that the family was being removed to remote regions of Siberia, for example, precludes an assumption, PERHAPS, they are in an isolated farm house. Further, when told that verified reports that the family are awakened, and shot in a basement... The imagery in the film may well be the royal Family's perception/imagining of their deaths. Remember, again, we are some years away from the benefit of the Sokolov report... Which even then was still filled with a lot of assumption and guess work. Earlier reports that the family are living under a harsh regime and some obvious deprivation, again it would be easy to assume they may be under a strict prison regime, "locked together in a room". I do not think it was laziness on the part of the film-makers to not try and make it realistic... I think that they only need to portray the perceptions the Royal family would be experiencing. The Romanovs are cut off, and there is little direct news to digest.
Further, the presence of the Romanovs in the film, serve, I think, as a further, and clear-cut reflection, of the "gilded age" of monarchy, as the final curtain of war and revolution sweep the entire old establishment away. Things will never be the same, whether the king in Great Britain retains his throne, or not. The movie clearly portrays the Old Queen Alexandra, and the rest with tear filled eyes.. Realizing the loss of their tether to pre-1914 world. Cousins Georgie, Nicky, and Willie will no longer rule that world.
I view the execution in this movie,in a similar, but much darker vein, as John's amusing idea that his Russian refugee cousins, might make a home with him. Filling the void of his lonely existence with the Tsarina, beating a rug, chasing a chicken, those lovely girls in the garden, and tea with the ex- Kaiser. Try re-watching the movie sometime from that standpoint. The flash scenes of the Romanovs in captivity, only come after George and Mary receive reports , obviously vague and thin, passed through the convoluted channels of war-time diplomatic corps and the Foreign Office. With that in mind those GLARING ERRORS are somewhat less chafing.