How to syncronize credentials in a small laboratory? (very slim alternative to ldap)

We run a small lab with 20 Linux systems (RaspberryPI, NAS, Desktop PCs) for research with 4 scientists who all need sudo permissions. We trust all 4 users as they have sudo permission and physical access any way. The laboratory network is a local network and not accessible from the internet. Now we would like to synchronize the credentials. If one user changes the password, it should not be changed manually on the other 19 systems. I would like to avoid complex solutions like LDAP. The first idea which came into my mind was to maintain the credentials on the NAS as single source and copy them via scp to the clients in a systemd module. But I guess I am reinventing the wheel and there are ready to use packages/solutions and I just tried the wrong search terms. Which package or solution is commonly used for such a scenario?