Well I should clarify before I address the ownership issue. I'm 'sort of' a moral realist because I think morality can be derived from nature, though not perfectly, because it is derived from us, which is derived from evolution, which cannot be predicted. If you are a theist that believes in a watchmaker god or at least believes that evolution is part of god's plan this won't pose a challenge to you. But there is quite a lot we can say about morality without challenge. Essentially Natural Law takes the low lying fruit.
So our morality is real because it results from reality. But the morality would be quite different, say, for intelligent beings evolved (assuming it is possible, which I don't assume) from herd animals, or solo predators, hive animals. (for reasons I won't get into now I think animals with more collectivist evolutionary strategies cannot win the evolutionary game)
If you think reality results from transcendent processes or agencies this still shouldn't challenge you.
OK, ownership by reality. Reality or morality do not 'own' us merely because when we act in discord to it we suffer consequences. If I own you, you don't get the choice. (this relates to my thoughts on free will too, but again I'll skip that) Since we are the ones who always have the choice, even if the choice kills us if we defy an evil state, if the word ownership is to be meaningful at all, it must first apply from an individual to that individual.
If god created a universe which rewards us for correct action that still doesn't imply ownership, anymore than an entrepreneur owns us by providing incentives for correct behavior. (that is not a claim that all entrepreneurs provide win/win transactions, but some do)
Still self-ownership has some subtleties when applied and expanded, which is one reason why I didn't include it in the piece. Your example of sovereignty for example can be put to rest with ethical symmetry and delgation without bothering with self ownership.
If the state has sovereignty then it must exist first in the individual. For sovereignty to be meaningful it must also be unalienable. It does no use to claim sovereign immunity if I just say, well yes I recognize sovereign immunity but I revoke your sovereignty, now answer the question! But if the both the state and the individual are sovereign then the best thing we can say about sovereignty is it's meaningless and the worse is that it is a contradiction.
Just on etymological grounds the word sovereignty implies ethical asymmetry. It sounds good, but the history of the word is in claims that some have rights and powers others do not. You can say every individual is sovereign, or as Huey Long said "Every man a king" but then what is the point of saying it? If we are all kings then not only is kingship is highly overrated, but are we then not just saying we are all human?
Better to say: "All men are created equal" with the understanding that means morally equal, not physically or materially equal.