The laws of Intestacy can be unjust and not what the deceased person would wish, which is why everyone should make a will, if there is no surviving spouse, the estate will go to the children who are still alive, then parents still alive, then brothers and sisters in equal shares. These categories are self-contained so that, if someone survives in any one category, the next category gets nothing.
You may remember Jill Dando, who was 37 when murdered, single and without children, she died interstate and her estate went to her Father.