Nope. Two faces cannot be added. Authentic video, as Apple itself admits its limitations.
It would be made better by software updates in future i guess. Few reports suggests, that Apple in order to speed up iPhone X delays lowered faceID accuracy, but Apple denied that claim (off course it would, as always)
From Apple official site.
The probability that a random person in the population could look at your iPhone X and unlock it using Face ID is approximately 1 in 1,000,000 (versus 1 in 50,000 for Touch ID). As an additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.
Source: https://support.apple.com/en-us/HT208108
Another detailed article about that kid and his mom:
At WIRED's suggestion, Malik asked his wife to re-register her face to see what would happen. After Sherwani freshly programmed her face into the phone, it no longer allowed Ammar access. To further test it, Sherwani tried registering her face again a few hours later, to replicate the indoor, nighttime lighting conditions in which she first set up her iPhone X. The problem returned; Ammar unlocked the phone on his third try this time. It worked again on his sixth try. At that point, Malik says, the phone's AI seemed to learn Ammar's features, and he could consistently unlock it again and again.
