Going to the original question:
"Can you tell me are two gate's are interchangeable?"
The answer is: Depends by your application.
Originally the Dual-Gate MOSFET was invented to get a gain-controlled device (input signal on G1, and DC gain-control on G2). Also this device can be used as an RF mixer, applying two RF signals to the gates, and output to the drain.
Generally the Gate1 of the device has narrower gate than Gate2, so has lower capacitance than Gate2.
The DC bias applied on G1 it will have less influence on the transistor drain current, than if is applied on G2.
So, if you use the device to mix two RF signals, the device might work if you interchange the gates.
But if the device is used as controlled-gain amplifier (input signal on G1, and DC gain-control on G2) you cannot interchange the gates.