Kao chan on renshuu is Kao chan and technically its legal name.
I kept it just Kao chan no nicknames because if I never write it down, I will 100% forget it the second new I finally understand new grammar particles or structures.
(And i have already previously forgotten the difference between は and が twice proving my awkward memory retention but somehow passing JLPT mock tests)
At best, I only call them by their final evolutions such as: (spoilers below. Description provided if you want a summary of what I actually call them without the actual names of the evolutions)