Multiple users on one paying account?

Hi there, I search Multiple Accounts and don’t feel this is resolved so start a thread again.
I am a freelancer working on a project with multiple other freelancers. We are all paying for separate licences separately yet cant edit the same document we are all working on (even though we all have a licence!) without being charged effectively twice! I have convinced the project owner that we need a corporate licence for all of us so we can all collab on the same document. Is that possible? If we all paying for a licence why can’t we do what we need?
I can’t seem to see how to edit my colleague’s work without being charged again! Please clarify! and help me find a solution to this basic thing.