Just a guess... It all starts with a SPST? And then you progress in steps until you have DPDT?
So once you put together a mosfet circuit to do SPST, duplicate it to perform symmetrical action (SPDT), and duplicate again so you have DPDT?
It's not readily obvious where the SPST section begins and ends, and what the control signals do. I think the control signal both biases the transistor, and adds DC component to the incoming signal (which is AC coming from the left-hand).
As for the DPDT schematic, there's two overlapped wires in the center, creating a kind of cross-biasing. I suppose the purpose is to turn on the left side which turning off the right (and vice-versa). Perhaps the purpose is also to add a DC component in the signal path.