Making sense of existing wiring for multiple switches controlling fan+light and separate light
Going in circles (without making a loop)

What you want is possible with the addition of a single extra cable -- a 12-2 from the light box controlled by switch 5 to the fan box.  Once this cable is in place (turn the power off first of course):


Remove the retagged white wire from its screw on the dimmer (switch 5) and move it to the terminal on the dimmer that's connected to the black wire coming from the orange cable (i.e. the black hot coming in from the fan box).  This is the only change needed in this box, so you can button it up now.
Nut the new cable's black to the existing red, white to whites, and ground to grounds in the ceiling light-only box -- this makes the new cable an extension of the red wire in the 12/3 from switches 2 and 4 to the ceiling light box.  This finishes the ceiling light box.
Nut the blacks from the red, yellow, blue, and orange cables in the fan box together.
Nut the whites from the red, yellow, and orange cables in the fan box together.
Nut all the grounds in the fan box together.
Nut the black from the new cable to the black from the fan/light combo.
Nut the white from the new cable to the white from the fan/light combo.
Retag the white from the blue cable to a hot with some black tape, and nut it to the blue from the fan/light combo.
Mount the fan and button everything else back up
Turn the power back on and enjoy!


Note that the white from the new cable is not nutted to the other neutral whites in the box as that'd create a looped neutral in violation of 300.3(B)/310.10(H).  Switches 1/2 form a classical 3-way switch loop controlling the light in the fan, while 3 and 4 are considered a T-loop (where power goes to one switch and the other switch is looped from the first switch's location), and switch 5 i.e. the dimmer is wired conventionally (vs. the utterly nonsensical traveler connection that it currently has).