Roles that match the job
Everyone signs in with their own account and gets a role. Owners and admins manage billing, connected channels and settings. Members write, schedule and edit posts without being able to disconnect an account or change the plan.
Clients don't need a seat at all for reviewing work. They approve posts from the client portal using a private link.
One workspace, many brands
Connect the channels for every brand or client you manage to the same workspace. The calendar, queue and analytics can be filtered to one of them at a time, so nobody posts to the wrong account and everyone works from the same plan.
Inviting someone takes an email address. They get an invite link and join the workspace with the role you picked.