You can use RefShare to share  references with anyone, even if they dont have a RefWorks account.

Other functionalities require that all researchers have an institutional RefWorks subscription, which means they are entitled to access RefWorks' accounts.

You will need to decide if you want to store the account on the University of Auckland's server, or the other institution's server. If you decide on the University of Auckland,  UoA users can log in through the databases page in the usual way but the non UoA based users will need to login via the main RefWorks page http://www.refworks.com and enter the University of Auckland group code RWUnivAuckland, and then the log in details.

Similarly if you decide to lodge the account on the other institution's server they will need to supply all UoA users with their institutions group code so UOA users can log in at the main Refworks site.

Users at seperate locations can log in to RefWorks or Write'N'Cite using the same log in details.

The issue is more about how to share your document in a mutually accessible location, and ensuring administrative control and backups are in place to avoid overwriting etc.  As with any processes requiring collaboration, clear communication and guidelines are required.

Shared drives are an option but where this is not possible, consider using shared areas such as Google Drive. This makes it easy to upload a Word document, share it with others and then allow them to download it and work on it on their own PCs.   It's probably best to come up with mutually agreed practices for working on documents so that it is easy to identify the latest version of a document.