Symlink photos? How not to "Copy" but leave photos in place?

Once you get the hang of it, it’s easy to use Bridge and Lightroom Classic together on the same set of files, I do it all the time. The basic steps for this are below. Some of this was already covered in this thread, but there are some details to follow to ensure the data fully goes both ways:

1. Import the folder into a Lightroom Classic catalog, and use the same catalog so you aren’t always making new catalogs. If you’re already looking at the folder in Bridge or the Finder desktop, the fastest way to import is to drag the folder icon and then drop it on the Lightroom Classic app icon. This opens the Import dialog box for that item, skipping a lot of digging around in file dialog boxes.

2. At the top of the Import dialog box, Add is probably selected by default, and that is exactly what you want if you want to catalog the files where they already are (no moving or copying). So leave it on Add.

3. You probably don’t need to make any changes in the Import dialog box, but if you do they might be in the File Handling and Apply During Import panels. Otherwise just go ahead and click Import. (Tip: To minimize how large the preview cache grows with each import, in the File Handling panel, set Build Previews to Embedded & Sidecar. And set a low cache size limit in Lightroom Classic > Catalog Settings > Limit Preview Cache Size.)

4. Do whatever you need to do to those images in Lightroom Classic, such as place them on a map.

5. Very important: When finished in Lightroom Classic, select all of the images in that folder and choose the command Metadata > Save Metadata to Files. This is because Lightroom Classic saves changes to its catalog by default, so if you want Bridge to read those Lightroom Classic edits, you must use this command to make Lightroom Classic write the changes out to the XMP sidecar files/metadata block that Bridge and Camera Raw read and write.

6. Switch back to Bridge. It should automatically pick up the metadata changes, including any location (Map module) changes that you will now see in the GPS section of the Metadata panel in Bridge.

If you want to do this often, all you have to do is remember the implications of step 5 when going both ways: 

• From Bridge to Lightroom Classic, on import Lightroom Classic will read in any existing XMP metadata that Bridge/Camera Raw wrote for the files. 
• If files are already imported into a Lightroom classic catalog and you later edited them further in Bridge, in Lightroom Classic you must choose Metadata > Read Metadata from Files to update the Lightroom Classic catalog with the changes made in Bridge. 
• From Lightroom Classic to Bridge, when finished editing you must choose Metadata > Save Metadata to Files for Bridge/Camera Raw to be able to see any edits made in Lightroom Classic. 

In short, always make sure you understand which side needs updating, and use those Metadata commands to update the metadata in the right direction before switching over to the other app.

Lightroom does not copy the photos unless you tell it to do so. If you want to leave the photos where they are, then in the import dialog use 'ADD' at the top center. That will only add the photos to the Lightroom Classic catalog (which is a database, so the photos aren't really added to the catalog but a record in the database is created that only contains all the necessary information about the photo), without copying them to another place.

The issue I'm having is when I import using Lightroom Classic, I end up with another "Library" that has those same images which is doubling the use of disk space.

Not correct. Your photos are not in Lightroom Classic. Your disk space usage does not double. LrC does have to build previews, which take up a much smaller amount of space on your hard disk, and shouldn't be a problem.