Q: Old iPhoto Library

You should be able to delete the schools libraries, however Apple have found a way to make both the old iPhoto library and the new photos library access the same photo database there by not needing to take up the space twice.  If you delete the iPhoto library, you will save very little space by doing so and may ultimately regret it if you later find something has gone wrong in one of your migrations.

The last ones are almost heavy in GBs as the new ones. May I delete all the "iPhoto Library.migratedphotolibraries" to get more room in my HDs? Thanks a lot.

It only looks like you were using twice the space in the Finder.  All original image files and previews in the new Photos library are hard link copies of your photos in the iphoto library. the original and the copy are using the same blocks on your drive, but look in the Finder like identical files of the same size.

See:  Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

and Six Colors: The (hard) link between Photos and iPhoto

I would not burn all bridges by deleting the iPhoto Library just now - follow Winston Churchill's advice. At least keep a backup copy of you iPhoto  library.  We have seen several reports were it has been necessary to repeat the migration of the Photos library from the original iPhoto library, because the problems could only be fixed in iPhoto.

And Photos does not yet support all features of iPhoto.  You may want to add location data to photos or edit books or calendars you created in iPhoto, or batch change titles or captions.

'School's library'

Ha, that's dictation for you, or more correctly the lazy old fool that didn't check it properly.

Ha, that's dictation for you, or more correctly the lazy old fool that didn't check it properly.

Dictation is even more creative than the spellchecker.   You are brave! Sometimes it is really embarrassing how the software interprets innocent typos!

And the spellchecker cannot even correct "spellchecker" correctly. I just stopped it from turning my typing into "Speck checker".

I beleive you are correct that the spell checker is worse, but dictation eliminates it, so I prefer dictation.

Unfortunately I'm in the pub now, so it's back to typing. Well not unfortunately, but you know what I mean.