(Forgot about this but something came to me)
Disney researches their movies; for example, Moana stayed true to the Polynesian culture by visiting the islands and getting a hands on experience. Disney could easily send people to Russia-St. Petersburg and Moscow-to their Palaces and the Archives to learn about the girls. Or they can come to this forum, talk to people like Helen who have published books (diaries or not) about them. Maybe they can end/start it in 1911 at Olga's Ball at Livadia.
A nice idea with Olga's ball being the centerpiece.
However you need to ask yourself why would a production company like Disney make a movie about the Romanovs in the first place if they weren't going to tie it in with the dramatic events of the era.
If you're going to do OTMAA without Rasputin, Revolution, WW1, Ipatiev House, etc., what's the point of doing it in the first place...and doesn't it just become another princess movie? (Hamlet without the Prince?)
Of course we Romanovs fans might take kindly to the idea and watch it, but how do you go about attracting a wider audience? How would Olga & Tatiana be any different from Elsa & Anna? And what do younger girls (the primary demographic here) really care about historical accuracy?
Every Disney Princess movie is a Princess movie; I wouldn't want to let my children watch the mental torture of the Imperial Family (being locked in the house, painted windows, stuffy rooms that kind of torture) and then their massacre, so Ipatiev House is out of the question. Rasputin can be shown to be a kind man who gave the Imperial family hope instead of a walking corpse with magical powers and a tiny albino bat as a sidekick.
This movie can be before the Revolution, and the only historical inaccuracy that can occur is giving all/few/couple/one of them a love interest and an adventure to go on. Their can be references to history through the plot, and I can finally have a Romanov film that has Olga, Tatiana and Maria in it more who actually have lines.
Olga and Tatiana will be different to Elsa and Anna as they're not Scandinavian and Olga does not possess winter powers (unless she wasn't telling us something). Olga and Tatiana have a sister bond that rivals Lilo and Nani from Lilo and Stitch
, and much stronger than Elsa and Anna's definitely. Heck, their bond may rival any siblings in the Disney universe, so not only do they show a tight bond that sisters lack (myself for instance) but their different personalities would resonate inside someone who may show qualities they hate that Olga, Tatiana, Maria and Anastasia possess.
Your last question is the answer I've been asking myself since Anastasia (1997) came out. Do younger children really care about historical accuracy? No, but guess who did? Adults. Adults who knew about the Romanovs were angry at how inaccurate it was, but young boys and girls, mostly girls, didn't care. It was a children's movie, it will forever be a children's movie, but some people forget that and hate on it. Like Disney is an animation studio focused on making movies for children. It would be targeted for little children whilst making small jokes for adults who watch the movie. Children and most teenagers only care for the songs, dresses, the characters and animation style, they won't care about the historical accuracy and the plot, but like I said Disney tries to target adults as well, so they could put in some historical accuracies like hints to Alexei's haemophilia for example.