When two people fuse through the fusion dance, or the potara earrings, the newly fused product leans to the characteristics and personalities of the two former subjects, but they do not submit to their control. The only character who ever submitted to control was super Gogeta, who had no choice.
The pupil is a hole located in the centre of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.
Pupil is the opening in the central part of iris which is responsible for controlling light entering into eyes. So pupil dilates when the light is dim while it shrinks if the light is strong and bright. So in a dim environment, dilated pupils are very common and normal that you don't have to worry about it.