In response to paying to sit next to each other, your seats will be allocated for your party before you even come to the airport. If you come to check in early, there might be a possibility that your seat can be changed, however this all depends on who elses seats have been allocated, usually those who have paid to sit by each other or those who are not having meals. Don't expect to come at the end of check in and choose your seats as there more than likely will be no seats together for your party and you will have to make do with what has been assigned.