I think the experience of Lynda Bellingham's sons must be fairly common. According to news reports her widower had been asked to see that her sons were "looked after". That really is open to interpretation, isn't it?!
My great-grandparents were well off and owned several properties. They didn't make wills, but had made it clear to their three sons and two daughters, who were all very close, that everything was to be divided fairly between them. Of course, when the day came the eldest son simply announced that he was having the lot, which under the law of the time was perfectly legal. The fact that nobody in the family spoke to him again obviously didn't matter a jot to him!
In the early 1970s my father and his sister and cousins each received a solicitor's letter saying that my great-uncle had died. When his estate was being sorted out it was discovered that he had never had the property legally transferred to his name. They were all invited to put in a claim on the estate. I don't think any of them did.
And the moral of the story is.....get your wills sorted out, for goodness' sake!!