No standard law determines how real property is divided among heirs in a death case. In the US, this can vary based on state laws and what types of relationships a deceased person had to whom they were connected.
In Texas, the property would be split into decreasing levels of connection with the deceased based on such factors as who survived to inherit from them. The clearest example of how succession works is if there are two children who get into a car accident. If each child has descendants but no will, then the court will determine the legal trustee.
There is also the law that a person must outlive you by 120 hours. So if one sibling died only 2 hours after the other, then their descendants would not receive any of the property.
These types of tricky situations highlight the importance of having an estate plan in Texas.