Hi Bunny

There will more than likely be availability when you check in on line. For some reason, expertflyer sometimes only shows the rear economy section from about row 41 back, the more forward section shows up around 24 hours before check in. Whether this is held back or not (so they could substitute a smaller 343 if loads are light) I'm not sure, but I've seen huge changes in the seat maps in that last 24 hours.

As a family, they have to seat you together but that could mean 2 behind 2 (one adult and one child) or across an aisle. It is highly unlikely that they would seat one adult with the 2 children and one adult somewhere else.

My advice would be to check in online 24 hours before (and look at the booking from about 2 hours before that - sometimes the seat map becomes available earlier). If you are happy with what you get, print your boarding cards so you can go to bag drop. If you're not happy, use OLCI to bag the best seats that you can but don't print your boarding cards and check again at the airport.

What date are you travelling on?

Regards
R3dV