I suspect that the luck that was experienced by the guy who did the single ESC to two motors came via a good deal of experience and thinking, but given that the motors are well capable of turning their props, and the ESC is capable of handling the combined load and the battery is up to the job of starting the things, then the motors must stay perfectly synced with each other.
A fuse would need to be heavy enough to handle the startup current, but can only be between battery and ESC - no point in trying to fuse the individual phases of the motors. With more than one ESC, obviously, one fuse per ESC makes sense.
With sensible loading, in all probability, fusing can be reliable at much lower values than the motor spec suggests, and if it needs to be that high, a) can the battery supply it anyway for more than a few seconds, b) just how big a fuse mount can be carried?