Best Way to Organizer People Using Several Sub-Categories

And here are guides for using People tags and Keyword Tags.

People tags should only be used for identifying people with face recognition.  You can then add the subcategories with Keyword Tags or Albums or both. So you could have each child identified with a People tag, and all children tagged with a Portraits tag. You could then place all portraits photos in an Album.  The advantage of using an album is that it allows you to display the photos in an order that you can choose. 

What you want to do is not specific to any version of Elements nor to people data. For instance it could apply to any picture type like birds, minerals, landscape types, so use the normal keywords and categories/subcategories hierarchies.

- Also, to manage 'families' and 'family branches', don't only think strictly hierarchically, which can make searches harder. The search features are optimized for multicriteria. Better to assign multiple tags to the image of a person than 'storing' it in a hierarchy. Particularly, a person might be known by its first name, full name, second name, nickname, married name...

- If you are uing a genealogy software, you could store the identifier of the person as another tag

- Another powerful way to organize is to use captions extensively. That's descriptive, that enables storing multiple data in a single image. You can search for single words in a caption (or a note), for combinations of words in a single caption, even for parts of a single word.