You can choose the preferred type of seat (airplane seat, business, VIP) but not the exact seat.
Through the automatic online reservation system, shipping companies do not allow the selection of specific places.
In any case, the system tries to place all the passengers of a reservation in adjacent or nearby places if they are available at the time of your transaction.
However, this is not always possible, as this is a parameter that has been set by the booking system of each ship and we cannot control it. However, if not for all the passengers from the same reservations have been given nearby or close seats, you can ask the crew to assist you when boarding.