If the late Queen has set up trusts for her younger children those trusts would be beyond interference from The King.

If she had expressed a desire in her will that The King make provisions for his siblings from the fortune that he inherited from her it would be entirely at The King's discretion whether to honour such a request.

I think that the first instance is almost beyond doubt - it is an important way that the rich distribute wealth across generations.

I take your point about Andrew having, possibly, been a particular drain on the late Queen's finances during her later life, but I don't see how that could have been reflected in the Will, since she left The King the lot (lucky King!).