Does the male testicles grow at a same rate with eachother or does one grow first then the other one grows?

Same Time: They will grow at the same time, but you can have a slight size difference or hang difference and be normal. If there is a significant difference in size, then there may be something affecting the growth and it needs to be checked out. See your doctor.

Testicles: I would be interested in what would cause this kind of question to be asked. But, one of your testicles will be larger than the other. That one will be your dominant one that produces much of the testosterone and sperm. It is also a system that if one fails the other one can take over the duties.