With Clearstream you can have up to 25 Users per account/Subaccount. Each User only has access to the account/Subaccounts they've been invited to. There are 3 different roles that a User can have.
Owner - By default the person who registered for the account will be the Owner, but you can transfer ownership from your Settings. The Owner can do everything and has access to the master account and all Subaccounts. There can only be one Owner.
Admin - Admins can do everything that an Owner can except they only have access to the Account or Subaccount(s) they've been invited to. They also cannot create Subaccounts or edit Subaccount allocations. Admins can invite additional Users, edit Integrations, access billing info, API, and change your monthly plan (if a User in your master account).
Editor - Editors have access to all the core features in your account. An Editor can create and send messages, view incoming messages, and create/edit Keywords.
How to Change a User's Role
Steps:
Go to Settings.
Click Users in the sub-menu
Find the user whose role you'd like to change and click Edit Role.
Select your role and then click Update Role.