It is possible to generate a single custom report on the Palo Alto Firewall for various activities for a particular user or create a single report for multiple user activities.
Yes, This is possible by fine tuning the Query Builder under Monitor > Manage Custom Reports > Report Settings (give the appropriate settings).
The screenshot below shows User 1 added:
The screenshot below shows User 2 added:
The screenshot below shows Multiple Users added:
Users are added in the "or" function and will be able to see all the User Activity information in one single document. When the Run Now button is clicked a single report is generated.