Training + Setting up Microsoft Teams and Its Security Features

We are a small team of 5 members and have RECENTLY subscribed to Microsoft Teams. All team members work from home on confidential assignments. We have multiple Microsoft Teams subscriptions on multiple domains and would like to use all of them on one Teams client on the desktop.

I need help from someone to help me configure Microsoft Teams in a way that a team member can work on any file online that has been shared - but can't download it to a local laptop or share it outside the organization network.