You cant have 2 sites that uses the same data from the same database, because of how WordPress works (permalinks etc), i am guessing you want to do this to show 2 different themes, 1 for the desktop version and 1 for the mobile version, try doing that with 1 WordPress installation and change the theme based on the device with a detecting class either from a plugin or make one.
I recommend you to use a stylesheet instead of having 2 themes.