What is the best way to give some users access to workitems only in a project area?
One answer
I don't think you can achieve it easily this with the users organization you have. Components visibility (and so source code visibility) depends on the owner of the component (that could be a project area or a team area). The only way I see is that you create a team area that membered all the users that needs to view source code and then change the ownership of the components to this team area, restricting the visibility (it is a flag that must be enabled when you change component ownership).