When you configure the VM, you can specify the display number to associate with that particular VM. Add the line vncdisplay=“X” where X is some small positive integer. Then execute
vncviewer 127.0.0.1:X
will connect you to the appropriate VM.
Without the vncdisplay line in the configuration file, I believe that it assigns the next available integer value. The first VM will be on :0, then next will be on :1, etc.
vncviewer 127.0.0.1 is equivalent to vncviewer 127.0.0.1:0
You can determine what the display number is by using netstat. VNC servers listen (by default) on port 5900 + display number.