A few things to consider:
Bhaalspawn were a insurence by Bhaal. In order for him to return all of them must die, which happened in the lore when the BG2 protagonist got murdered.
Dragonborn only appeared after Bhaals death, so can't be Bhaalspawn. (Maybe when you count the transformed humans, but they were good aligned, transformed by divine power, rare and that also happened after Bhaals death, although here its possible that this was retroactively changed).
