If you have four people or less in your group and can fit in one sedan, you will only be charged the €23 per vehicle. The same applies if you have eight people or less and can fit in one minivan, in this instance you will only have to pay for one vehicle and not per person.
However, if your group requires two vehicles -- for example there are five members in the group so one has to take their own sedan -- you'll pay for those two cars.