Give most of the Palaces and other houses they own to the National Trust and give the proceeds to the country.
Are you extending that to all the people who own big country houses, say, Chatsworth, Blenheim, Woburn Abbey, Belvoir Castle, Floors Castle, Blair Castle, etc. etc. or do you just have the royals privately owned property in your sights.
And a little bit of googling shows that many of the royal residences owned by the crown are already open to the public.
Give the Crown Jewels to the V&A for exhibition.
The Crown Jewels are exhibited at the Tower of London and have been for all of my lifetime.
Either insist on actually approving what the government put in from of him before he signs it, or do away with the archaic tradition of Royal Assent all together. Along with the State Opening of Parliament.
But the republican proposals for a non royal, apolitical, HoS always seem to include a requirement for approving legislation 
Give all the profits from the Duchy of Cornwall to ... err...Cornwall.
No comment
Limit titles to one per person - e.g. you can't be Prince of Wales and Duke of Cornwall. Pick one.
Why?
If members of his family want to support charities, encourage them. Just don't pay their expenses when they go to visit them.
How do you know that they don't visit them and take an interest n them in their private capacity as well?
Buy bikes for William and Kate and the kids to get around on.
I'm sure they could afford their own bikes...
Throw out those blooming ridiculous uniforms they all seem to have stashed in the cupboard.
Gosh, those uniforms do rankle, don't they? I expect you'd like to throw out all the ceremonial uniforms of the British armed forces. (The provision and upkeep of which, incidentally, no doubt support a number of thriving private enterprises)
Come on, volver. You can do better than this, surely?