Nice I like the Idea, and it does sound a lot like ravens, but it's all original. The story line for helping the ghosts for weapons bigger than Legendary is something I think we can all look forward to.
You said:
Quest: Not going into detail, but it would involve helping the crew defeat Jollys Army, and in return they would give secrest to finding Forbidden weapons to defeat Jolly Roger. These weapons would be more powerful than legendary weapons, and the background would be black. Other than that, I have no idea what the skills would be, although each would have TWO special skills.
Hmm, A special on a weapon that would increase health, and endurance while summoning the rage of 13 ghosts and a burst of ghostly strength like the oragutang cutlass

??
Quest idea:
How about Pirates brings back true undead flagships like the Phantom, or better the Death Omen Flag ship..
shivers. I I can imagine Widow Threadbarren having a family heirloom aboard one. Only you can't get it off the firt one, ye got to hunt for it.
Remember the old Maurauder Quest