You still have to pay the actors and actresses the residual fees for using their voice work, and you would further still require some talent to do new recording work because you don’t necessarily have a whole library of archival recordings for all 1,000+ Pokémon.
Financially and practically it...
You have to follow the three of them around the school. Look at any transport console in the school and see where each one is waiting, then find them, talk to them, and repeat. It's a whole sequence that needs to be done for each character before you unlock being able to visit their dorm rooms.