Q: Help me understand managing photos with Photos app

I need help better understanding how I am supposed to manage my library of photos the “Apple” way. I migrated from Microsoft to Apple about a year ago and did the same to my wife earlier this year. I copied over to her iMac our library of thousands of kids photos (about 85GB). Since then, I’ve tried to manage the photos the same way as I did on Windows. What we had done in the past, and continue to do, is the following:

• My photos are synced to Dropbox, so at random intervals, I move my photos from my Dropbox to her computer and I delete the photos manually from my 6S Plus.
• Use Image Capture to extract images from her 6S to her computer.
• Up until recently, I then used Image Capture to delete the photos from her phone. This was a two-step process, until Sierra and it appears the option to delete photos has been removed. Now, removing the photos from her phone is a manual process.
• All photos are stored in monthly subfolders in her Pictures directory (i.e. /Pictures/Family Pictures/2016-10
• Photos (and other files) are then backed up to the cloud via Crashplan and to an external drive.

While this has been an involved process, it has worked. Until recently. When I turned on the “iCloud Photo Library” option on her phone. Then, all of a sudden, 5000 photos that were apparently on her computer in the Photos app were synced back to her phone. I since have disabled the setting, but the prospect of going back through and deleting those photos from her phone is not appealing.

Also worth noting…. We use the Shared Photo Streams heavily. We have about 25 shared streams (adding about one every month) to share photos with each other and 6-8 family members. I like that a low resolution of those photos are stored on our devices and only if viewed. It’s amazing how the 19,000 photos and videos in our shared photo streams only take up less than 500MB on my phone.

There are some consequences of managing photos the way we do. For example, the new “Memories” tab is always blank. Also, just the overhead in extracting images from both our phones is exorbitant. But, I also have concerns about the way the Photos app on macOS appears to store the photo library in a single file. How does that work when your library starts to grow in the 100+ GB area? I know I am not alone with huge photo libraries.

So, hopefully that is enough info. So, how should I be doing this? How can I consolidate the photos that both my wife and I take into one library? Is what I am doing acceptable? Is there a better way? How do I ensure photos are backed up?

I know this was a long post, and I appreciate it if you read this far. Thanks in advance for any advice.