Lord Coleridge is simply inverting the actual order of things.

Half the existing "rules prescribed as to the possession of property" have, for their ultimate object, the protection of family life, the privacy of the private home, and the provision made by parents for their children.

But family life is not primarily the creation of prescribed rules.

It is the creation of instincts and affections which have developed themselves in the course of ages.
Instead of the law creating family life, it is family life which has gradually called into being--which has created and dictated--the rules and sanctions protecting it.

The same is the case with bequest, marriage, and so forth.