Whoa, you've had quite a journey getting those 5 Photos libraries sorted! As you know, Apple Photos uses a database structure, storing the unedited versions of all photos and videos in Originals folder within the Photos Library.photoslibrary package. Within this folder are sub-folders named e.g. A-G, 0-9 etc., and the file names are GUID based, which bear no relation to the original file names. To export everything with the original file names, there are two ways, both quite easy:
1) Using Photos app's export functionality: Create a folder for each library in the destination drive. In Photos app, select all the photos, then click File > Export N items > select the options (e.g. metadata, file naming convention etc.) and export. If you have photos in iCloud, download them to the Mac before doing the above. Repeat with each library.
2)
Using Photos Takeout for Mac: This app exports Mac Photos libraries into folders by years or albums. If photos are in iCloud, it'll download them to the Mac and then export to the destination drive (So you must have enough free disk space). Like Photos, this app also retains original file names (or Titles, if you've added any) as well as metadata. The evaluation version is free, so see if it works for you.
With both the method, you can preserve your album or folder structure. Good luck.