Cannot log in after Mojave upgrade (10.14.5)

I recently upgraded a Macbook to Mojave, and have not been able to login to any of the two accounts set up on the machine. From the login screen, certain characters weren't working - I could type an upper case I, but not a lower-case i, for example. Resetting PRAM seemed to have no effect.

When I restarted in recovery mode (while resetting PRAM), I was able to put in the old passwords and create new (vastly simplified) passwords for both accounts. Once I restart out of Password recovery mode, however, even the simplified passwords don't get me passed the login screen. If I go back to recovery mode, however, the simplified passwords work to unlock the disk.....

The Startup disk only has Mojave on it, so I can't restart back under High Sierra.

I was really hoping on taking this machine a 2 week trip abroad, but right now it's just a pretty brick with a login screen I can't get past.