I found two ways of sorting bookmarks:
Take one or more bookmark folders and drag them to your desktop. This puts them into Finder and automatically alphabetizes them. From here you can also delete duplicates, rearrange, etc. Since I had thousands of duplicates, this was ok but would take a long time.
2. I eventually found a little program, Bookmacster, for all osx versions and bought it after trying it and being delighted. It cost $22.95 and is worth every penny for someone with my problem. The website is: http://www.sheepsystems.com/products/bkmx/ The developer is helpful, too.
Since I'm no longer so ignorant about how iCloud works, the duplicating bookmarks problem shouldn't return. If it does at least I have Bookmacter to help.