Someone can correct me if I am wrong, but I don't believe so. You can have a domestic partner, but there are all kinds of hoops to jump through. You will have S3C priority on all metal except your own, which you will have S3 but DL mainline can still bump you as it goes by seniority. Parents also pay what is called a yield fare, so they don't travel free.

The only ones I know of that have decent DL benefits is SKW. They can have a enrolled friend, buddy passes, S2 travel, and they bump DL mainline on their own metal. Parents also fly for free.