The cameras have an internal clock that is a basis for triggering the frame read-outs.
According to the answer in this topic
https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=96762 they also have a separate internal clock for audio.
It is possible to jam sync the cameras, meaning that you connect an external TC generator for a short time, so the internal clock sets itself to the exact time of the external TC.
If you do this with multiple cameras, their internal timecode is in sync, which is very useful for multicam editing.
But the stability of the internal camera clocks allows the multiple cameras to stay in sync for only about an hour without having an external TC generator connected.
So you can sync multiple cameras for about one hour with only one external TC device.
If every camera has, say, an Ambient NanoLockit permanently connected, their timecode stays in sync for as long as the NanoLockits are in sync and connected to the cameras.
The external timecode should take over the internal camera clock.
If this is also true for the internal audio clock would be interesting to know.
One question that remains is, if the cameras could be close to being phase locked if the external TC sync is VERY precise.