I'd like to know if it is possible to run multiples RPA robots in the same Windows VM with different login account. i.e.: 1 Windows VM; 5 user accounts; 5 "OpenSpan.Runtime.exe" instances (for each user account).
No, this is not advisable. In practice, you are still running your applications under a single VM and a series of complications can arise from trying to run multiple Runtime processes concurrently. This is most definitely not a supported configuration.