A lot of houses won’t run off 120V/20A. You’ll also need to kludge around the fact that your house wants 120V/240V.

In any case, serious V2H should support much more than 2kW. An EV with a charger with less than 6kW capacity is almost unheard of. Two EVs should be able to supply twice the current. All that’s technically needed is an charger that is physically capable of operating as an inverter (which I believe adds little cost), some way to derive a neutral (the usual solution is a relay and an autotransformer, again not particularly expensive), and the control logic to convince all of the above to actually operate in this mode.