I need help creating a breeding system with males and females. And also shoals and groups.

Hello, I need help to do two things
#1: Automatic Reproduction System: To make the Automatic Reproduction System, I want a Creature that is the Female, When it touches the Male that is Another Creature, the Female Turns into the Pregnant Version, How do you do that?

#2: Shoals or Groups: How Do I Make One Entity Follow Another Like the Shoals of Tropical Fish in Minecraft?

Any Help Would Be Appreciated