What's wrong with "Iono kepo haedar urnesi"?
While I can't say how a Valyrian would view that formulation, hāedar is the nominative, not the accusative singular form, which is hāedri.
Why is it ñābri instead of ñāmar? I thought ñābri was plural?
The accusative singular is identical with the nominative plural for -ar words.
I think the plural would end in a long I instead. "ñāmar" is the nominative singular, and the word is in the accusative here.