I think it would be a good idea to further the family options. I think it would be useful to have an option where you can become the brother/sister to an original lastname owner.
Example: Dunadan Estel has founded the last name "Estel." With a family option, someone would be able to become the brother/sister of Dunadan, take on his last name, and have it as info in there whois. "Is the brother of Dundan Estel." All with signed confirmations for both people of course.