1
Context menu
When you are inside your organisation's chat click on the cogwheel next to your organisation name and select "Manage Members".
2
Active Tab
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.
3
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).
4