Call reservations and have them iron it out for you. Munich Marriott reservation page lists their rooms as having 1 King or 2 Doubles. Their rooms can accommodate 4 guests per room.

Did you perhaps mean the Munich Airport Marriott, their rooms only come with a choice of 1 Queen or 2 Twins. If you had entered 4 Guests/Room when attempting to book a reservation at this hotel, you would have received a message indicating that this hotel cannot accommodate 4 guests per room.