Are these really iPhoto libraries you want to merge into a single Photos library?
Are you running Ventura?
Where is your Photos library located? Is it on a volume that has enough room for all of the iPhoto library together in the Photos library? If not, copy it to a volume with sufficient space.
Then open the Photos library and go to the File menu and select Import. Navigate to the first iPhoto library to be imported and import. Check the import before deleting the iPhoto library to make sure all photos and videos were successfully imported. Then do the next iPhoto library.
If you've put a lot of organizational effort into the iPhoto libraries, i.e. folders, albums, etc., you may want to use the paid version of PowerPhotos to merge the iPhoto libraries into the Photos library. The following is a comparison between Photos and PowerPhotos regarding merging libraries.
PowerPhotos: Photos:
Albums -----------
Smart Albums (as regular albums). -----------
Folders -----------
Captions Captions
Titles Titles
Original images Original images
Edited images Edited images
Locations Locations
Favorites Favorites
Can detect and exclude Duplicates detected after import
duplicates (or not) during import
Neither method included projects.
Both methods could import older iPhoto libraries into a Photos library when the iPhoto library couldn't be migrated into a Photos library.
