Wow, that's alot of cool ideas :-)
Looking at the suggestions, Occultist and Spiritualist would be out as we don't have the Occult Adventures so the GM, quite reasonably, won't allow it.
Ditto with anything Unchained unfortunately.
Order of the Tome Cavalier is definitely an option as the party has a bunch of scrolls and being able to use those would be a bonus and full BAB is always nice.
The Undead Scourge Pally would fit the setting really well, also.
Some sort of Alchemist also looks like a definite option as I hadn't realised just how flexible they could be so I could tweak it to better suit what the group is going to need.
Really appreciate all the help guys!