According to this [Wikipedia Link](https://en.m.wikipedia.org/wiki/Treaty_of_Constantinople_(1533), Charles V and Ferdinand I lost their rights to be called emperors to Suleyman. They were supposed to be equal in rank to the Ottoman Grand Vizier with the Ottoman sultan being the only emperor in that region.
They are emperors of Holy roman empire (germany) not bizantine. The first is a legacy of Charlemagne, the second a Roman.