Taking it as true that Deco - and whatever other assets (e.g. real estate) - were worth some millions prior to the death of the father, it is a virtual certainty (as in, 99.9999999%) that the father had an estate plan prepared for him.
By far the most common plan is one by which (1) Deco - and whatever other assets - would be lodged in corporations whose shares in turn are owned by a so-called holding company that was owned by the father, (2) the shares of the holding company would be placed in a so-called family trust, the trustees of which would be the father and one or two or three other people whom the father would expect to 'do what he would do' after his death - such as the mother - and (3) the terms of the trust would give the trustees discretion about what to give to the kids from time to time (including to give some of them more than others). The father's will also would provide that whatever property might pass by his will (rather than being in the family trust just described) would be held by trustees for his estate (probably the same people) on similar terms (and, IIRC, it was said by some source that the estate of the deceased father was valued at something like $5 million).
The end result is that, on his death, most of the father's wealth would be held by the family trust (and, therefore, would not pass by his will, and so would not attract probate taxes - what people call 'death duties') and any other wealth he had would be held in trust under his will. Therefore, aside from salaries paid from Deco to the kids (it seems, as of now, only Randy and Doug Jr.), all of the income generated from the father's wealth would flow through the family trust and (to a lesser extent) the trust under his will. The trustees would be quite able to put Rob, and by connection to him Renata, on a more modest 'allowance' than is given to the mother or to Doug or Randy, or even to Kathy.
I suspect (but can only suspect, of course) the the trustees are the mother, Randy (despite his history, he is the eldest kid, and he passed the lie detector test) and Doug, and perhaps a fourth person (such a the father's lawyer or accountant - not Hotmail lawyer, or I'll eat my hat) and that Rob (and by association Renata) are kept on a short lease (in $$$ terms) because they cannot be expected to manage money wisely.