Automatically logging in multiple users when Mac is booted


This is a follow up to my last question about syncing iCloud Photo Library.

My Mac file server is setup, that the user for running the plex server is automatically logged in. But I also would like to automatically log in a few other users, so that their iCloud Photo Libraries get synced to the file server for backup to backblaze.

My question: How can I login multiple users through a script which should run as a login item of the plex server?

Any suggestions?