Two of them have also been ordered to avoid the inner-city bar and restaurant where the offending took place.
Detective Senior Sergeant Scott Anderson of the Canterbury Adult Sexual Assault team said the case highlighted the importance of taking care of each other when on a night out.
"It's crucial that when you are out socialising, you keep an eye on your drink and stay on guard for this type of criminal activity," he said,
"But it's also really important to look after your mates – if anyone feels drowsy or suddenly 'out of it', take them to a safe place, and don't leave them alone."
As the matter is now before the courts, police are unable to comment further.