and the last file (which you can see is a video clip). When I try to open it in QuickTime though, it won't open.

What is the error message in QuickTime Player?

In QuickTime Player go to the Window menu and select "Show Movie Inspector"

The Inspector will show you the codec for the Video in the Format line.

What is the codec?

You can assign actual Lat/long coordinates in Photos to give precise location - you can not control what Photos calls them

LN

In Photos ==> preferences ==> general set click on "use as the system library"

LN

No direct way - simply export from LR including the desired metadata imbedded the the EXIF/IPTC fields or with a XMP sidecar adn import to Photos

LN

ran the update to the OS from iTunes and Photos App is back! 

My concern is the possibility that the High Sierra version of Photos may make some modifications to my photo libraries that are not backward compatible to Sierra.

Yes it is - pretty much every update of the OS does - you need a separate coy of the Photos library for HS testing - once you open a Photos library with Photos 3 in HS you can no longer open it with any older version of Photos

LN

1. Where are you trying to share the pictures from: the Photos app? iPhoto for iOS? Another app?
2. What happens when you try to share to Mail: is the option not there? Do you get an error?
3. What is the iOS version number currently installed on your iPad mini, located under Settings > General > About > Version.

You can nest folders as deep as you want

for example

trips

   US

      new york

      Missouri

  europe

     italy

     France

         Paris

         South of France

         Britiney

Etc - no limit on nesting

What exactly is the issue you are having?

LN

You install new apps (including the OS) from the App Store

LN

The person album for your son may be hidden. You hide persons by deleting the album. To add a hidden album back select a photo of the person, where the face is circled and view it enlarged. then swipe up to reveal the faces thumbnails below the photo and click the thumbnail with the face of your son to open his album. At the bottom of the album click "add to people"