On the open-source version, there is no "workspace" per se but If I understand you correctly, I think they only need to have access to the same shared folder. You would need to configure proper permissions for each user at the operating system level.
I believe it is not possible to share the same RStudio Project though, because metadata would get corrupted or overwritten among users. A better way to manage this scenario is to use version control with a centralized repository (like GitHub) that way each user works independently but commits changes to the same centralized project repository.