I also rely mostly on Google Photos as my viewing and sharing app. This includes sharing photos with family which is done through Google Photos shared albums.

I'm really the only one who cares about archiving photos so I'll transfer the shared photos from Google Photos to Google Drive (using the "share" functionality from the mobile app).

This kicks off a workflow that simultaneioously organizes the shared photo into my library and copies it too Dropbox and uploads it to my Google Photos library [1]. (I use Google Drive as a transport mechanism to get photos off my phone and onto my Synology).

Not ideal but once I got it set up it's worked really well.

[1] https://github.com/jmathai/elodie/tree/master/elodie/plugins...