I's suggest considering a Honda EU of 5000 watts or greater and having an electrician install a slide lockout plate in the main electrical panel. The slide lockout either the generator circuit or the utility input to be activated, but never both at the same time. Either way the house will have all of the circuits live and available, although some discretion in usage will need to be exercised when on the generator ...especially if the house has a well pump and/or heat pumps.
The new Hondas can be started remotely wirelessly, so all that would be needed to be done when the grid goes out is to flip the fool proof lockout breakers over and start your Honda from your phone.
A second alternative is to consider the purchase of one of the new bi-directional EVs that are coming out. Ford was the first to announce this with their existing F150 hybrid and the coming Lightning pure EV. VW has also announced that the second wave of their ID4 will be bi-directional. The rest of the EV manufacturers will no doubt soon follow.
And third, consider installing solar with a battery backup. We use the SolarEdge
Energyhub system but there are a ton of really good alternatives available. Use the one that your favored local installer recommends. By going this route you gain the security of instantaneous fully automatic backup when the grid goes down, the security of knowing that you will have a generally reliable power source (the sun) when fuel may not be available due to either a severe weather event or grid hacking, a constant reduction in your monthly utility expense, and the long term financial benefits from the ITC and asset value of the solar array and backup system.
The quickest and easiest system for your relative is the Honda with a
slide lockout and with minimal maintenance it should serve their purpose well for years to come