Originally Posted by
lehovec
Out/In bound treated as two different flights, even if booked together, so no, you will no be split up. If the remainder of your party are on the same booking seats will be together if available when checking in.
That's not quite correct. Although all 5 will be given adjacent seats at check in, the 2 actually travelling may be separated by a row or up to 3 seats (plus aisle). When the missing three aren't flagged through security, the seats allocated to them may be given away to strangers.