Hi Mouser,
Dont pay the "sit together" scam just get to the airport a bit earlier and you wont have any problems.
Charter companies try to frighten people into paying this, the worst I have seen was flying out of Gerona with My Travel a couple of years ago. At the hotel one of the first things the rep tried to do was sell this to families saying that the airline can now seperate children as young as eight from their parents, we ignored it, and going back were one of the last to check in and suprise suprise we were all sat together.