As a small team, you probably don’t need an Organization plan. It’s a plan for large companies with many teams. Create a team and invite two of your designers if you haven’t done so already, then upgrade it to Professional plan with 3 Editors.
As you all are members of one Professional team and you are Editors on this team, you would be able to create unlimited files and projects (folders for files) within this team and work in them together in real time.