Investigate D8 options for Groups.

OG is not ready in D8; discussion here:  https://www.drupal.org/node/2591017  There is a new module called Group, which I heard on a podcast is quite good:  https://www.drupal.org/project/group    ...but need to check it out.  Also, how to simply do it with entity references (which is mainly what OG is doing).