What wire is needed for a double 3-way switch on fan/light
If you're going to use wiring similar to the first diagram from that thread, and you're planning to use 12 AWG wiring. You're going to need five conductors (plus ground) between the switch boxes, so I'd probably use two separate cables.





In the case that the power originates at the fan/light, I'd make use of some 12/2/2. Using a length between the fan/light, and first group of switches. Then another length between the two groups of switches.



NOTES:


Grounding conductors have been excluded from the diagram, to make it a bit clearer. Make sure all grounding conductors are properly installed.
Notice that the white wire that's being used as a traveller between the switches, has been reidentified at both ends using a bit of black tape/marker/paint.
As @Wolf Harper points out, make sure the two cables between the boxes stay in close proximity with each other. Or use conduit with single conductors pulled through it.