That's incorrect. The Royal Family subsists on its own income. Even when it got the civil list monies, that money was in lieu of income from the Crown Lands.
Unlike the Kennedies and other American royalty, the Royal Family pay their own way. Also they very rarely suffocate people in lakes!
And where did their income initally come from? Hereditary privilege and position, and lands owned by the crown. It was stolen 150 years ago and more,,, and now they are insisting they live on “their” income.
This would be like NAZIS melting the gold teeth, investing the gold,, collecting the profits,, and then claiming they “subsist on their own income”.