The iPhone X apparently can't tell the difference between twins
https://www.neowin.net/news/the-iphone-x-apparently-cant-tell-the-difference-between-twins
Back in August 2015, a similar test was conducted on Microsoft's Windows Hello feature. Contrary to the iPhone X's results, no wrong twin was given access to the computer used.
Despite reducing the accuracy of the face-recognition sensor, Apple claims that the technology is still superior to the current Touch ID. It remains to be seen, however, if and when Face ID will gain better face-discerning capabilities.
https://www.neowin.net/news/the-iphone-x-apparently-cant-tell-the-difference-between-twins