I think the first line in the subjunctive mood, not the dative case of the indicative mood. May thou rest... is a hope (subj.), not a statement (indic.) or even a prediction(indic. or conditional). I don't know if this changes the wording any further. (I remember a textbook accurately describing the subjunctive in English as "moribund," but the language of her rhyme is supposed to be archaic.)

If I were writing something like that, instead of "been disowned" (meaning "had one's birthright taken away") I would say something like "been released," or "been disencumbered," or "been freed." Or "abdicated" or "cast off [or "passed on"] thy load."