GND of 9V batteries in a circuit
You won't get "a lot of power" out of two 9V batteries because they don't have it.

Outside of that, the circuit will work.

The "REF GND" is particular to the simulator, and you don't need it in real life.

You connect GND to the ground of the rest of the circuit, and that's it.



Back to the 9V batteries.

They have a capacity of a few hundred mAh.  If you draw more than maybe 100mA, then they will be drained in a very short time.

They are not designed to deliver large currents, and cannot do it.

Further, you are using linear regulators.  They work by throwing away power as heat.  Using linear regulators, you are wasting a large part of the little energy that  a 9V battery can deliver.