I still dont think that theory is true but the biggest clue to support it would be the end credits. Here is part of that map
here is link for bigger view:
https://i.gyazo.com/c3b7540aea42e8956610eda8db2fec3d.jpg
I dont think any of the other ppl in previous films are descendants of the skyview survivors:
1. The main reason I dont think it's true is because the parents of the main character for FD1 is still alive.
2. Those other films were other mass casualty events not one offs. Death isnt gonna kill 50 other ppl just because one descendant isnt pose to exist.
3. If they were setting that angle up, they wouldve purposely mentioned it in the film.
4. Death doesnt act the same as the first film. In the first film the protagonist can "save" ppl from their "death" and it can skip them in the cycle and go to the next person. But it would come back around. In the below clip the main character is saved from his "death", it skips over him and kills the next person.