This summary is not the rule. The rule text controls.
When someone dies and their estate is being handled in court, there's usually a person in charge called a succession representative. This person acts on behalf of the estate. If someone wants to sue over a debt or obligation that belonged to the deceased person, they need to name this succession representative as the defendant, not the family members.
The heirs or people who are set to inherit from the estate don't need to be part of the lawsuit. This is true no matter what kind of case it is, whether it involves property, money, or both. It's also true whether the heirs live in Louisiana or somewhere else, and whether they have someone representing them in the state or not.
The main point of this rule is to make lawsuits against an estate simpler. Instead of tracking down and naming every single heir, the person suing only needs to deal with the succession representative. This keeps the estate's business organized under one person while it's still being settled in court.
There are some exceptions to this rule, which are covered in other parts of the law. But in most everyday cases, this is how it works.