Yes. It's a pointless uphill battle to try to change people who don't want to change. The employees have a lot of leverage by not documenting the mess. If they leave you will take the blame.
Get another job ASAP. Let natural selection do its magic.
The "employee" lock-in played a heavy part too. No documentation meant they had significant leverage - it was an 8-person team who worked together for nearly 15yrs.
Get another job ASAP. Let natural selection do its magic.