How far apart can the cameras and hub be?
That will all depend on how many walls (incl. density and construction materials) you have in your home between hub and camera(s).
The Moobox app has an WiFi strength indicator so you will know very easily if the signal quality between camera and hub is going to be strong enough for consistent operation.
If the signal is weak just tweak the camera position relative to the hub. This may take some trial and error to get right as each user's circumstance and environment will be different.