Q: Managing 2 macbooks, 1 w Iphoto, 1 w Photos, iCloud

There are photographs in Photos on my MBP 2015 that I want to add to an IPhoto library on my MBP 2008. (They are also in my iCloud but apparently that's irrelevant.)

So I am looking for a simple way to add them an iPhoto library on the MBP 2008.

I should add that I have Fat Cat iphoto file manager and the Fat Cat manager for Photos.  I'm trying to think of the most efficient way to get all of these photos (constituting the ENTIRE Photos library) copied to my macbook 2008 iphoto library.

It's 5 G of photos.  (I mistakenly downloaded everything from my iphone into Photos.)

I keep thinking of things to add -- sorry. Once I'd downloaded them to Photos, I can't download them again to the other computer running Iphotos. So I hope there's some way to do it in bulk.

Gotcha (in a vague way; I have a lot to learn).

I realize now that I need to get a better sense of the relationship between my iPhone, iPhoto, Photos and iCloud Photos. Please bear with the tedium of my descriptions; it's the only way I can figure out where I am and how I got here, and it might be helpful to someone else who might have the same question or, even better, might have some answers where I put question marks below.

--Sometime this fall after I got my new computer, I did something that instructed iCloud Photos to immediately show a copy/thumbnail/image of any photo I took with my iPhone. I'd like to know how I did it. [?]

--I connected my iPhone to my new computer and apparently downloaded/imported every photo on my iPhone to Photos (5 GB, going back to 2009, many of which I'd already imported to iPhoto and not deleted on my iPhone) I didn't delete any of them because I thought they'd still be available to download/import to iPhotos on my other computer. This was a big mistake, because I depend so much on the Faces feature in my work.

--Every photo I now take shows up immediately on iCloud Photos. That's fine by me though I need to understand the implications re icloud storage.[?]

--If I connect my iPhone to the old computer running iPhotos, I can open iPhotos and download/import any photo that I haven't already downloaded/imported to either iPhotos or to Photos on the newer computer.

**Even after I import to iPhotos, those pictures continue to show up in iCloud Photos. So it shows all photos imported directly to Photos AND all iPhone photos taken since xxx even after imported to iPhotos.

I clearly need to understand more about what iCloud Photos is and why it shows photos imported to iPhoto -- would you have a link that might be helpful. [?]

[?] It wonder if it would be easier to export from iCloud Photos [or download?] which I can see on my old computer alongside my iPhoto library, rather than trying to do it from Photos on the new computer? If so, would the instructions be the same as those you sent me?

Thanks for your help,

Mary

Found it: iCloud Photo Sharing FAQ - Apple Support