Well, when I talk about isolation, it means that how well the switch can block the high power from receiver side. However, if the back to back MOSFETs switch is used, the isolation between the sources to the driving circuit is also required because the voltage on the source would follow the high-power side voltage during the negative half period when the switch is in off state.
To FvM: low resistance is because the receiving signal is very weak, almost at the same level of the thermal noise of 50ohm resistor. Large resistance would introduce more noise and comprise SNR. I wonder the "switching" stages structure you mentioned. Do you have any schematics? Another question, the T-circuit you mentioned, does it mean two mosfets back to back or something else?
Also, I checked some photovoltaic couplers' driving ability. Turns out it is too slow for the big power mosfet which Qg is around 50nC.
How do you think of the transformer coupled driving circuit I found? Does it sound reasonable?
Anyway, thank you guys for all the help.