Yes, you can.
In order to book a whole cabin for you and your travel companions, you will have to select the same accommodation type for all passengers. If the 'whole cabin' option is available, please select 'whole cabin' from the drop-down list. In case the 'whole cabin' option is not available, you can select the 'bed in shared cabin' option and passengers will be separated according to their gender and we cannot guarantee that will be placed in the same cabin.
Figure 1: Whole Cabin Selection
If you select the same accommodation type for all passengers, you should see the phrase '2-, 3-, or 4-bad cabin' in the trip summary (on the right-hand side). This verifies that you are booking a whole cabin.
Figure 2: Whole Cabin Confirmation
Kindly note that the limit for cabin capacity is usually up to 4 passengers. Of course, there are two options. The passenger can purchase a whole cabin or book a bed in a shared 4-bed cabin (not 2-bed), with passengers of the same sex. It should be mentioned that in most cases the number of passengers must agree with the number of beds, except for some exceptions (e.g. Grandi Navi Veloci).
Please keep in mind that for most ferry companies Infants do not occupy a separate bed in cabins and an economy class is automatically assigned to them.