Recently on Facebook, All members on Facebook group can comment on a post. But as for Now Facebook has introduced new features to empowered group admin ability to turn off a member ability to comment or post. 
This new features give admin of the group ability to remove anyone who violate thier community's group from the multiple group they manage in a single click. Facebook now added a new tools to make it easier for group admin to write a welcome post that will automatically tag joiners. 
In additional, Facebook also introduced a new features called members profile. This features lets members click on another person name and it will be directed to a group-specific profile, base on publicly available like things they may share in common and S feed of that person's activity in the group.