photos and iPhoto libraries

Hi

First - the iPhoto library. When you opened it it will have been migrated to a separate Photos library which should now be in your pictures folder.

Second - to open different libraries, hold down the option key while starting photos. This will bring up a pane that lists all the libraries on your system, and allows you to choose one to open - it will also tell yo which is your system library. Your system library is the only one that will sync with iCloud.

Third - how to merge:

1 - Take a backup of all your libraries. You need to be able to backtrack if anything goes wrong.

To merge libraries you can use iCloud. The basic process is to set each of your libraries as the system library in turn and enable iCloud for that library. The contents of that library will then be synced with what you already have in iCloud (and in your current system library)

2 - For all libraries excluding your current system library:

3 - Open each, starting with the smallest.

4 - Open preferences, and click the button "use as system photo library"

5 - On the iCloud tab of preferences, make sure iCloud photos is enabled.

6 - Wait for the sync to complete - this might take some time. Days (or even weeks for a large library). And bear in mind the library you are syncing will grow to the combined size of it + whatever you had in iCloud before you started to sync it. So you will need plenty of space on your system drive. Sync is complete when the status at the bottom of the all photos view says "updated just ow"

7 - Repeat for each library.

As to the problem with your iPhoto Library - when you open an iPhoto Library, Photos will create a new Photos Library from it, with the same name as the old iPhoto Library. The filename Extension of the iPhoto Library will be changed to .migratedphotolibrary . This way Photos can tell, that the library already has been migrated and refuse to open it again. Probabably your iPhoto Photos are already in one of your Photos Libraries. If the photos are missing, you can open the iPhoto Library again in Photos, if you rename the filename extension of the library back to .photolibrary .