Moar ideas:
Patchouli: CheyTac Intervention (camper; called unmoving great library for a reason)
Nitori: ACR with suppressor, ACOG sights, extended mags, and an M26 Modular Accessory Shotgun System (she's an engineer so it would make sense that she would mod the hell out of her gun)
Meiling: QBZ-95 (the Chinese girl needs a Chinese weapon)