My house is 60+ years old, with original cloth wrapped 2-wire 12 ga wires throughout the house, and an updated 200A breaker box. I wish to replace a 3-way switch setup on a ceiling fan/light with a double 3-way switch setup - a 3-way on the light and a 3-way on the fan. I am looking at using two Leviton 5640 in the existing single-gang spots, while replacing the old boxes with old work.
I planned on wiring it up based on some homeowner's how-to books, like this diagram shows. My question is what wire should I use to replace the existing 3-way setup, while adding for the double switches? I've wired a fan/light on a double switch before, using 12/3 with a ground, but I didn't know what wire I should need for the double 3-way setup.
From best I can tell, I need a hot and ground going to the first switch, 4 feeder wires going to second switch, and a 2 hots and a ground coming from second switch to fan/light.