I know human has a complete rebuild kit but for a fair bit of cash and id need two kits to get at least two of them working.
No, you only need one. The kit has four woofers, four tweeters and two xovers. They list the price as "per pair" which may be confusing given there is a pair of drivers in each cabinet, but the kit does a pair of cabinets. It's not cheap though.
https://www.humanspeakers.com/e/parts/k202e.htmEdit: Oh I get what you are saying now. You would need two kits for all four cabs. Seems like a perfect opportunity to experiment. You could do one pair with the kit and take one down the upgrade path then compare when finished. I would be curious to see/hear how the upgrade compares to the original.