Photoshop elements conversion and consolidations with NAS

Those are not "dummy" questions, they are extremely important to manage your library and catalogs safely and easily.
You don't state it clearly, but I understand that you have a single catalog and that your "library", the photo files, is stored on different external harddrives. If you have several catalogs, we'll have to consider different solutions.
You want to move the files to a single, bigger storage. That's a common requirement an even the oldest Organizer versions offer two simple ways to 'move' the photo files from one drive to another.
The simplest one is to use the folders 'drag and drop' in the left folders panel. You select the master directory of one external hard drive, drag and drop it on a destination folder on the big common storage drive. That moves the folder with all its subfolders just like from Windows explorer or Mac Finder, with the difference that the new location is automatically updated in the catalog.
The safest one is to create a full backup and restore it where you want, in this case in the destination folder of the big storage disk. No move, only a copy of your photo files folders AND a copy of your catlog in the new destination folder. It's obviously safer, you get two copies plus a full backup! That's the usual way to proceed to move your catalog and library to another computer or drive.
helpx.adobe.com/photoshop-elements/kb/backup-restore-move-catalog-photoshop.html

You'll notice that no 'import' is used in those processes. No change in your catalog exept the location of the files on the new drive.

If you "import" files, you get the tags from the files themselves, not from the catalog which is the only only one storing albums, stacks, version sets, creations... Even if you "write metadata to files" you only recover the keywords, captions and ratings. That's why the solution when upgrading is to "convert" the old catalog to the new format. Converting a catalog updates it, but does not change anything to the photo files themselves. The converted catalog will still show the files in their original location.

If you have a single catalog, the result of the two above solutions will be that your catalog will be updated to the new location: each older external drive content will be shown in its own new folder. Existing duplicates will still be there. Removing duplicates is not a simple task, there are lots of discussions about what you can do; it would be best to discuss this in another thread.

That's another question. Both above solutions apply to any kind of drive used to consolidate the contents of your external drives. The common solution is to use a couple of external USB drives, one for storing the library, the other one for backups. That's simpler, cheaper, faster and safer. The organizer has never been created to use NAS; you can use them, but you won't get any help from Adobe. So the computer gurus advising NAS should also be knowledgeable with the organizer. There are a number of traps with using NAS. I won't be able to help you there. A totally safe solution with your present hardware would be to use the NAS as the backup drive. Safe and easy. Maybe one of your present external hard drive is big enough to store all your library? 1 tB external drives are common and cheap today. Other external hard drives may be big enoug to be used as additional backup drives stored outside of your home (friends, relatives...)

Please come back for more details, especially if I am wrong in thinking you have a single catalog.

Ok so I looked a bit more on the older computer my photos in PSE 13 are in catalogue 2(about 27,000) and photos PSE 14 are in catalogue 1 (about 750) with some overlap. is there a easy way to merge those catalogues into just one?
As far as I can tell, all the photos are on the NAS in photo folder (each date has its own sub folder, so there are many).
In the new computer PSE 15 there is “my catalogue” that has 54000 photos (twice as many as PSE catalogue 2 which makes me suspect Some dummy ,me imported them twice) and “photos catalogue” that has about 1700 photos
It sounds like your recommendation is to back up photos to NAS but put the actual photos on external hard drives and access them from there. Can PSE store only the thumbs on new computer and then I tell it where the actual photos are (ie the hard drive) and work on the photos from there? That should save hard drive space on new computer.
It also sounds like the best plan is to merge the PSE catalogues from old computer back them up to an external HD or NAS and then convert them to PSE 15 on new computer. Does it make sense to backup all the photos from PSE 15 on new computer and then erase all photos in PSE 15 on new computer and start fresh?
I’ve made quite the mess here,
Thanks for all the help