Factual error: The opening scene of the Skyview collapse takes place on May 16, 1968, according to a newspaper clipping about the tower being closed for repairs as a result of Iris' premonition. During the vision, when the first bodies fall from the sky, the parking valets are listening to "Raindrops Keep Falling on My Head" on the radio. However, that song was written for the movie "Butch Cassidy and the Sundance Kid" and wouldn't be released until October 1969.
Factual error: Surgical steel, which is used for making all kinds of piercings, is non-magnetic; therefore, the scene where the overcharged MRI instrument is tearing out Erik's piercings from a distance is absolutely fictional.
Answer: At no point does the film say they are descendants; you must have seen that in fan theory videos.
Iris tells Stefani she disrupted Death's design by warning Paul and the guests to leave the glass floor before it broke. As a result, the tower never collapsed, but Death began killing the survivors and their descendants, who were never meant to exist.