If you belong to more than one workspace, everything you see is scoped to whichever one you are currently in.
Switching
Use the workspace switcher to move between them. Your websites, scans, dashboard, team list and settings all change to that workspace.
Check which workspace you are in before you start a scan, particularly if you keep similarly named sites in more than one. It is the single most common mistake people make with multiple workspaces.
Adding someone who is already on your team
If a colleague already belongs to one of your workspaces and you want them in another, add them directly from the workspace you are adding them to. They do not need a second invitation and they do not need to accept anything again.
They can hold different roles in different workspaces. Somebody can be an Admin of the workspace they run and Read-only in another they simply observe. Their role in one says nothing about their role in another.
Inviting somebody new to a particular workspace
You can invite a new person straight into a specific workspace rather than adding them to your main one first. Useful when a contractor is only ever going to work on one client.
How this counts against your plan
People are counted once each across all the workspaces you own, so adding the same colleague to three workspaces does not use three places. Adding three different people does.