Can I move the .git directory for a repo to it’s parent directory?

You can do what you are describing like this:

1. Move the content of ABC to an ABC/ subdirectory, and fix the history so that it looks like it has always been there:

   $ cd /path/to/ABC
   $ git filter-branch --index-filter \
       'git ls-files -s | sed "s-\t-&ABC/-" |
        GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
        git update-index --index-info &&
        mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' HEAD
   

   Now your directory structure is ABC/ABC/your_code

2. Same for the content of DEF:

   $ cd /path/to/DEF
   $ git filter-branch --index-filter \
       'git ls-files -s | sed "s-\t-&DEF/-" |
        GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
        git update-index --index-info &&
        mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' HEAD
   

   Now your directory structure is DEF/DEF/your_code

3. Finally, create the PPP repository and pull both ABC and DEF into it:

   $ mkdir /path/to/PPP
   $ cd /path/to/PPP
   $ git init
   $ git pull /path/to/ABC
   $ git pull /path/to/DEF
   

   Now you have PPP/ABC/your_code and PPP/DEF/your_code, along with all the history.

You should probably ask you collegues to run the previous commands on their system, in order for everyone to be synchronized.

Note: the funky filter-branch commands come from the man page. 🙂