Because the family, rather than the individual, is the basic unit of society, then it must be acknowledged that the institution of private property is valid if and only if it benefits the family first and foremost, ensuring its stability and contributing to its development.
It is a most sacred law of nature that a father should provide food and all necessaries for those whom he has begotten; and, similarly, it is natural that he should wish that his children, who carry on, so to speak, and continue his personality, should be by him provided with all that is needful to enable them to keep themselves decently from want and misery amid the uncertainties of this mortal life. Now, in no other way can a father effect this except by the ownership of productive property, which he can transmit to his children by inheritance.
If conditions arise such that private property is somehow appropriated by individuals while families are left either without property or dependent on a few rich individuals for their survival, then it would become clear that private property was no longer serving its end, and it would open itself to just criticism.
 RN, 13.