Do they hear beeps?
If that is because of the battery then they should be hearing beeps.
I agreed with you that code management is a must for your case.
Have you tried another lock code management handler?
I believe there are at least 3 of them, One is called generic, one is paid, one is having schlage in its title.
Here you are if you’re willing to try each:
Wink, although have official support, there are also people experiencing battery problem.
I myself always use eneloop rechargeable battery for critical devices because I have tools to measure energy consumption when replacing them.
Another thing you can do is contact Schlage, their service is pretty good.