You are correct about Moments > Synology Photos. Shows how long I've been using them.
You might be missing something or I'm not fully understanding the question. If you perform a manual upload them you can choose your location. The automatic upload you can choose a default location and then move them around from there.
We use this as a solution for my family of 4. Each of our cell phones are automatically backed up to our respective folder/library. We then have the ability to share photos.
https://app.screencast.com/djMrnKe3sXWmz
Then we have another "shared" space and this is where we upload all of our photos from digital cameras, etc.
https://www.reddit.com/r/synology/comments/17a2c7a/we_love_you_synology_photos_please_keep_getting/