The money is in a trust and the trust is the owner. A board is set up to overlook (decide on) the investments (assets) and the spending of the beneficiary.
The beneficiary (eg Petra, or Petra and Tamara if they share, but I am certain each has their own) gets a monthly "allowance"/payment, but if they were to want anything big and that would need a good chunk out of the trust's money (for a house, yacht or whatever) the board gets together into a meeting to decide whether they'll grant this (based on the financial goings and the beneficiary's spending habits, because if the beneficiary is a spendthrift a good board will step in and curb that, J Depp above was one such spendthrift and bankrupt thanks to that).
The board is made up of.... Some finance person, friends, family, depends whom you choose.
The health of a trust depends on the beneficiary's spending, a trustworthy and responsible board and good investments (to keep it growing).
No death tax (which I think is daylight robbery anyway), since the owner is the trust and the person getting the money just a beneficiary.
This is a cliff notes version of a dummy (ie me), so there might be holes there, but this is the gist of it.