How Do The Behelits Work?

I’ve watched both anime adaptations, and just started reading the manga. Guts is currently killing the snake baron, who calls himself an apostle. During the fight Guts asks for the apostles of the god hand. My question is how do they become an apostle that’s not apart of the core god hand 5. Is it that the god hand is full so everyone else that uses a crimson behelit jus become a rando apostle in the world or did they use a normal behelit and there is only 5 crimson ones in total?