dng files downloading too pictures drive on Mac and stopping my computer from operating

[defaulti4fp89xyps0q]

1. I’m working with a number of external drives with various catalogs in them. 
2. When working with one drive Alby2 the memory of my MacBook for what appears to be no reason filled up with all the dng into my pictures folder with Files from that drive. As this virtually filled up the 1 tb of memory it stopped my LRC and everything else in the computer. 
3. What also has happened that all the files in that drive appear to be disengaged from my hard drive.
4. Spoke with Apple and they helped me remove all the excess files & I put all the dng files onto another drive. 
5. Thinking I had resolved it I started looking at my images in the new catalog that I had created from the files that had filled the memory and once again the Mac drive filled up again.

Can someone please help me sort this out as I’m not very technical. 

[defaulti4fp89xyps0q]

sorry number 3 should read disengaged from my lightroom catalog

[Rob_Cullen]

You are posting in the Lightroom (Cloud based) forum yet you talk of catalogs (plural)

So please give some details  of your app and version number in an info report  Main Menu > Help > System Info...

You also mention "one drive Alby2" - Is that the Microsoft OneDrive. If so it is a Cloud storage method, and Lightroom-Classic (If that is what you are using) requires local copies of your photo files, hence the need to have files located on your Mac HD or a local attached drive. Lightroom apps  do not work well with 'OneDrive'!

And why are you creating multiple catalogs?