Ceiling Fan Bracing

Good eye.

The only way to do this is conduit between switches

Unless you can find 14/5 with also ground.

The neutral and all four travelers need to run in the same cable or raceway (conduit). That's because the neutral is the return for all the travelers.

You can't parallel neutral as ThreePhaseEel discusses.

Or, keep them separate all the way

Your other option is separate them at the first switch, then, keep them separate after the second, with two 1x/2 cables going to the fan/light.

But since the neutrals can never rejoin, the two neutrals must be carried separately all the way to each device. so if the fan/light only has a common neutral wire, you cannot use this option.

Alternatives

You could use relays, as long as you keep your neutrals separate up to the relay coil. Or you could use 24V relays, either with combo relay-transformers, or by poaching 24V off your doorbell or furnace. Then your switch wiring could be 24V and use common thermostat wire.

You could use smart switches, so the power switching only happens at one switch, and the request from the other switch is handled by data rather than multiple travelers.

When I have attic access and need to add an electrical box for a fan or light I use two pieces of wood. One is made long enough so that it lays flat across the tops of the ceiling joists. The second piece is made to mount under the first piece but be on edge. Typically this second piece needs to be cut for width so that its bottom edge comes right at the level where the top of the electrical box needs to be located. Both pieces are cut from 1.5 inch thick framing lumber. The top flat piece is screwed down through the top ends into the tops of the ceiling joists. The other "on edge" piece is screwed to the top piece down from the top of the flat piece. The screws that hold these pieces in place should be respectable size and length screws installed through clearance holes and into pilot holes. For 1.5 inch thick lumber I typically use 3.5" #10 size screws.

This makes for a very sturdy mount for an electrical box even for fan mounts.

There is another significant advantage to this approach. It does not put sidewise pressure or pounding on to the ceiling joists. Such pounding and pressure can cause blistering of drywall finish on the ceiling where screws or nails are holding up the ceiling drywall.