Except DoW didn't pay any inheritance tax on a massive fortune.
Sorting the finances out, for me ( and I haven't fully thought it through) would involve:
Returning asetts to the control of the Mountbatten Windsor family, so that they can structure the disbursement of wealth to members other than the Heir and Spare.
Agreeing which assetts the MW family own ( e.g. Sandringham) and stipulating that, from now on, the family money needs to pay for their running and upkeep.
Agreeing which assetts ( e.g. Buckingham Palace, Windsor Castle) are state-owned and maintained, and the capacities in which the HoS can access them.
Agreeing a salary for the HoS (and the HoS-in-training), and the perks that come with it.
Cutting all public funding for the rest of the RF.
So the taxpayer ends up paying a salary and work-related expenses for the Monarch and Heir only; the rest of them get their family-wealth trust fund, and can get a job if they want.
Typo edits