An average EV battery is what, around 70kWh? Add in a bit of charging losses and we'll say maybe 75kWh being generous here, and that's assuming a nearly dead battery to a full charge. Doing that every month is then 900kWh, or 0.9MWh/yr. That's ~4% of the energy usage of 21MWh/yr.

An average EV gets what, ~3.5mi/kWH? An average US car does ~12,000mi/yr. That theoretical average EV would then use ~3.5MWh. Two would be ~7. But this author is in the UK, where the average car only does ~7,500mi/yr or so or a little over 2MWh/yr. So for their two UK cars, assuming they drove an average mileage in an average EV efficiency, they would likely have used something like 4.3MWh/yr for their cars. About 20% of their total electricity usage. This drops a good bit if they're really getting closer to 4mi/kWh in efficiency, which is likely if they're not driving on many highways like one does in the US.