Ha, we've been doing the same thing for the past few months! I just made a generic Immich account that we all log into and upload to that. I auto backup the library to other places as we go, just in case. Once we're done, we'll all get copies of the directory to do with as we please.

I have Immich set up to keep the name of the files instead of giving them a random name. As we scan we name the files with the peoples names and generic tags like Tom.Mary.Birthday.1992 and putting Mary before birthday indicates that it was Mary's birthday. So that if I decide to try and add meta data to the files it will be easier.

I haven't figured out a plan for adding meta info to the files so they at least have the year/month they were taken and I don't know if I even want to since we're 1000's of photos in now

Would Plex be an option here? I don't use it, but I know it has a photo library feature.

I haven't tested it, but did you look at Damselfly? The documentation seems to suggest you can do it: https://github.com/Webreaper/Damselfly/blob/master/docs/Multi-user.md

https://damselfly.info/

Couldn't you use immich external library? The only thing after that is a wayto upload sftp, email monitoring, web upload, or syncthing? Could do multiple options of these.

resourcespace? -> https://www.resourcespace.com/