For a trust created by the old boy during his life time, or by his will, that would depend on the terms of the trust declaration, or the will.
I find it singularly hard to imagine that the old boy would have provided that if Robbie is a trustee, or executor, and dies he is to be replaced by whoever might be his spouse at the time of his death, or by Renata specifically, as a trustee, or an executor. She is, as you say, not blood, and not someone that the old boy probably could even have got to know very well before his death.
As to $$$, it seems to me unlikely that she would have a right to payments from the trust, or trusts. I have seen a lot of wealthy people's trust declarations and wills over the years and it is far more likely that, as Rob's spouse, she would be eligible to get payments, as would their children, if the trustees, or the executors, so decide, so that the trustees, or executors, would have discretion about how much (if anything) and when. Indeed I would expect that the situation of 'his 3 sons' under the trust, or trusts, is the same; if anyone has a right to get payments it is most likely to be Diane.
It is my understanding, from Crazy Town, that Kathy is the beneficiary of a separate trust (originally $1 million) set up by the old boy, and that it is on terms that make Diana and 'his 3 sons' the trustees and give the trustees considerably discretion about how much Kathy gets from the trust and when (reflecting, no doubt, the fact that Kathy was a heroin addict, amongst other things, for years before the old man's death).