The guarantee of your family being seated together on a flight isn’t guaranteed. The airline will however try its best that you and your family are seated together when a booking is made for more than one person of the same group, at the same time and on the same flight. This is once again not guaranteed. The airline offers seat selection for a small fee at the time of booking. This is one of the best ways to ensure that the family will be seated together, not separately. If you however don’t want to spend on seat assignment then make sure that check-in is done as early as possible for increasing the chances of the family being seated together.