I can't see Lenin having a big role at all. In reality he was only a factor in the lives of the IF in literally their last year, call it 2% of N&A's lives. It was a huge role ultimately, insofar as he had them all murdered. But as a player in the Family's life overall, he wasn't. Most of it was spent in Swiss coffeehouses or otherwise in modestly-lived exile. He was a nonfactor in the 1905 Revolution. He was a nonfactor in the February Revolution. When he first arrived in Russia, the Romanovs were already under house arrest. He didn't aggressively move for a coup (and that against the Prov. Gov., not Nicholas) until the fall. Even in power he was more concerned with resisting real threats to his rule, and they weren't the IF in Tobolsk iin Siberia or even iless in Ekaterinburg. In his writings he rarely mentions the Romanovs as real people, only as the generic oppressive monarchy to be destroyed. He didn't even profess to be too vengeful for the execution of his brother Alexander in 1887 after the failed plot on Alexander III.
From Nicholas point of view , Lenin was just another would=be revolutionary, to be dealt with by the Okhrana and police. Nicholas never mentions him by name in his writings.
In this N&A, as well as in Romanovy, and in other movies/series, Lenin has been , in my opinion, reduced to a stock figure, usually huddled almost leeringly conspiratorally with other caricature Bolshevik biggies like Trotsky and Sverdlov, almost rubbing their beards with malice in determining the IF"S fate (execution).When the time came Lenin did order the IF"s murders and that , of course, is simply huge in their history and almost the prime way we remember them. But as a dramatic, ongoing character in the longer IF saga, Lenin really wasn't. It could work insofar as a drama needs a villain, but I think it takes too much license with the Romanovs' real lives.