A229: I guess, strictly according to the rules, when one of the Dvati runs through that Rite, the other one would just cease to exist, making that level adjustment totally worthless. I personally would think that, in RAI, since there are two distinct bodies and one collective soul, the two would both want to take the Rite, and they would both participate in separate rites and become two Dragonborn creatures.
Even if the Dvati keeps two bodies, they can't speak Dvati without that mental link.
EDIT: What ever happened to asking a 'Simple Question'?