So this was my father's bitcointalk account. There's also wallet.dat and a text file:
bitcoin.org
bitcointalk.org
The password is THE DATE
13zEUPdpCDT3JGqv4o61vXQpgWWdxMEZeX
The coins are still there. I guess I can try some dates
Did you maybe try the date your father registered on this forum? Given that the text file contains the name of this forum, it may be about that date.
Date Registered: 23 August 2015, 12:45:31