The close-up exterior establishing shot showing Felix's windows do not match the interior window design shown in the previous or next scene. In particular, the window frames in the first and third shots bisect all the windows at the same point, but in the close up it is about 2 feet higher in the middle window.
Sarah's mother claims she was paid in the UK to have a baby for someone else, as happens in the USA. However, this is not legal in the UK and she speaks about it as if it was done legally.
When Helena calls Sarah for help from the cage, the phone she is using is held upside down. You can see the main screen, which shows the time upside down towards her mouth.
As Helena is raised to think she is Ukrainian, her name would be either Yelena or Olena as Helena doesn't exist as a Ukrainian name. If someone with that name were to live in Ukraine all the same, the name would be pronounced Hgelena.