Which flight will likely have empty middle seats or an empty row?

Looking at NYC-KEF flights for this summer. Which flight do you think will have more likely empty middle seats in economy?

EWR-KEF
A) UA using 757 with 3-3.
B) Icelandair using 767 with 2-3-2

JFK- KEF
C) Icelandair using 737Max8 3-3
D) Icelandair using 767 with 2-3-2

Wife and I travelling with two tweens. So, if we do get middle seat empty, kids mostly will be the once laying down. Also, what will be the best strategy here to get an empty row?