Time for the Reds to Trump All Reds.
These Reds break your theory.
To really smack the hammer in.
Astrid did not kill Arya or Adolin.
The only time people entered the Basement between the times when Astrid locked the door and Astrid unlocked it was through the window.
The group entered the Guest mansion once, and it was through the front door.
All entrances were locked when the group arrived at the Guest mansion.
The Guest mansion has only two floors: the Basement and the First floor.