thats pretty correct. start one engine, turn on generator , load battery, turn off again, start the second and at lets say 30% ,when the current from the starter dropped , kick the opposite generator in.
Actually that's not correct. If his King Air has a triple fed bus system like he says and the POH doesn't say anything about turning off the generator then you absolutely don't have do it. Yes you need to let the battery charge but once the generator loads have reduced to at least 50% then just activate the starter ignition switch.