If a user logs into the iSeries from iNav, a job named QZRCSRVS in subsystem QUSRWRK will start and you can see the user profile there using WRKACTJOB. A QPWFSERVSO job that services a request from iSeries Navigator will also start in subsystem QSERVER.
Why would you want multiple users with the same profile name ? It is a very unhealthy procedure.
If you need to have users with say QSYSOPR authorities, create a group profile or an authorization list and assign users.
You can use the DSPUSRPRF or DSPAUTUSR command to generate a list of users.
The Navigator should be able to identify the users without problems. I am not sure why you cannot identify specific users.
Try WRKOBJLCK QSYSOPR *USRPRF
This will show you all the jobs that have that profile locked, meaning logged in. You can then review the job Job status attributes to identify if they are batch or interactive or some other type. (PJ, prestart is the type of job Navigator resolves to)