When Ainsley replaced the original soul, that soul was still a toddler who knew nothing. However, in those parallel worlds, they might have grown up.
[Even the same version as you, who is a transmigrator, might also want to come to your world to replace you for a lot of reasons.]
[If your other selves were treated worse than you because of their transmigrator identity, wouldn't they envy the current you? So, just be careful.]
Chronos and Aetheria were actually just scaring Ainsley to be more vigilant because a parallel world journey needed the joint effort of the two fairies, not Aetheria alone or Chronos alone.
To be able to get the two fairies to help the traveler would have already filtered out more than 99% of people in various parallel worlds.
However, since Ainsley herself was outstanding, her other selves might also be as outstanding as her, so there was indeed a chance that they could get the help of the two fairies.