To write a report to joint private clients (e.g. Mr & Mrs Smith) go to Write report, and add both clients into the Selected client(s) list and click Next step. 

The first client you add will notionally become the 'primary client' and as such their details will be displayed first throughout the report

If one or both clients are existing clients that have previously been saved to the Client Library, you can locate and select the client(s) using the client search. If one or both clients are new clients, you will need to add them using one of the three add new client buttons. This will not only add them into the Selected client(s) list, but also save them to the selected user's Client Library for future use.