As far as I know, you cannot run the same emulator twice, but by creating two separate emulators, you can run them simultaneously.
You create new emulators using the Android SDK Manager ("SDK Manager.exe" located in the Android installation directory). "Virtual Devices".
Then you can run them on the command line with
emulator -avd <avd_name>
: https://developer.android.com/studio/run/emulator-commandline.html