Second photo library shared via iCloud?

Hi everyone.

I currently have two photo libraries - one is the default which syncs just fine via iCloud to my iPad and iPhone photos app from my Mac. I have a second library (they are both in ~/Pictures/) which is not the default library. I can open it just fine on my Mac and import pictures to it, but I can't sync it across to my iPad and iPhone, which is very annoying because I'd like to edit photo sets in the second one from time to time from my iPad (I don't use the iPhone nearly as much for this). I tried moving the second library (Styles.photolibrary) to ~/Documents, but it won't sync and it won't open there. I'm wondering: How can I sync it to iCloud so that I can open it up on my iPad (and iPhone too from time to time?).

I don't want to merge them because they're huge collections of different retro styles and architectures from online which I collect for working on and inspiration. Putting them in my personal library would just make it a huge nightmare of a mess - even with tags, etc...it doesn't matter. It would just be too unwieldy.

Any recommendations? I'd rather keep using Apple Photos to edit and manage them for both libraries the way I do on my Mac.

Thanks in advance for any input.