When you are inside your organisation's chat click on the cogwheel next to your organisation name and select "Manage Members".
On the next screen you can browse all active users. You can check if they've activated Two-Factor-Authentication and you can remove them.
Inactive users tab
This tab shows all your currently invited users that haven't joined the organisation yet and users that have been deleted (but not removed from the database).
Further you can manage your teams from that page.