"The Lost Prince" portrayed one major inaccuracy in the Romanov death scene I'm surprised all you experts missed, which I'll discuss in a separate movie thread. Here I'll just touch on a few things.
Prince John doesn't seem to have been seriously retarded or mentally ill, due to his ability to be very up on people and write them letters asking questions specifically about those people. I got this not from the movie but from an article about him. He is known to have met the Romanovs, and the filmmaker was obviously caught up in the romance of their story perhaps to the point of overemphasizing them a little, but if Prince John was really so up on all his royal relations and they had a boy exactly his age--only about a year older--and people all over the world were fascinated with reading of the Romanovs, it seems almost more surprising that Prince John would NOT spend a lot of time thinking about them. I thought the overshoe scene was a bit over the top, but the barnyard scene was great--they looked so lost!
Queen Mary came off more as being very busy with the war and royal duties, than as being uncaring toward her child. The movie very humanely portrayed that moving to a private house in the country, besides saving the royal family the possible disaster of a public epileptic seizure, was the best possible thing in the world for Prince John. What would endless high-pressure state occasions have done to a poor sick child who could stress out chasing a parrot? Peace and quiet were the prescription for him.
I'm not an expert on the royals, but understand that both Queen Victoria and Empress Alexandra had German as their mother language, spoke it at home, and in the case of Empress Alexandra's children, they knew German as well or better than Russian as it was what they heard at home all the time. Don't know about their English but that's interesting about Nicholas's English being so good.
If anyone is near a library with old copies of "Saint Nicholas" magazine, there was one with an article on Nicholas as a kid of 16 or so.