This is a pretty isolated issue heh. In the west, you're only referred to buy your first name, not last or first depending on how close you are to the person, so the three guys wouldn't be an issue. For the girls, we would refer to them as Sakura S., Sakura O., etc. If multiple guys had the same first name, we would just refer to them by their last name only. Simple and easy. But for each system, it's own issues.