It is not possible to create subgroups inside of a group on Edthena.
To facilitate focused, small group discussions inside of a larger group, the best option is to:
- Define the groups users should participate in inside of the group description, through a message sent to the group, or in an email
- Ask users to include in the title of their video what group they're in, so that other users know whether or not to watch and comment on that video