A post that goes to accounts in several profiles can be seen by a teammate with any of them, but only changed by someone with all of them, so nobody can change what goes out on a brand they do not work on.
The Team page lists what each person changed in your account, newest first, for 90 days: posts made, edited and deleted, accounts connected, automations switched on. It also shows when each teammate was last active.
Remove a teammate from the Team page and they lose access within a minute. Their posts stay in your account. If your plan changes to one without teams, teammates lose access straight away and get it back if you move up again.