Posted June 7th, 2017, 07:36 AM
I have only used a car service within a city (airport to hotel, cruise port to hotel): Blacklane, very reliable. No clue what it would cost to have them drive from Munich to Passau or if they would do it at all. Unless your group has handicapped members, I don't understand why they don't want to use the options available that everybody else uses: rental car, train, city cabs.
Train is "the German thing". Have the hotel call a cab with a driver willing to park and take you and your luggage directly to the train platform. Of course, he needs to be paid for that special service. Alternatively, book Blacklane for this personal service. Pre-arrange the same service in Passau. There is another service called mydriver, but I have no personal experience with them.