This is how I see it: (I can only remember Bada's and Doha's names, forgive me lol)
No the others are players, just that by removing their own tapes they use to save they lose memories and act like the characters they are supposed to be in the game. Bada has ALWAYS been an NPC in the game, not an external player possessing the characters, and they just dragged him to play with them. As for the others, from what I understood Bada started playing with them only at the point when Doha and the other dude were the only one left because the best friend guy told Bada that in the earliest memories he had Bada wasn't with them. Seeing as they should have all been awake at the beginning of the game when NPC Bada is supposed to warn them, and Bada has always been that NPC, I don't know if that guy didn't actually see his face at the time and therefore didn't know Bada is the NPC or if he was lying about not knowing Bada because he didn't want to shock him or something? Idk
sooo if npc can gain sentience by inserting the tape could that actually mean that they were ncps for some time too? or how does this work??? and if not then why there's only one npc in their team then and it's pi bada??? and did others know that???