Thanks for all the advice. We know it's going to be uncomfortable. That's why we've delayed travelling as long as we could, but we can't postpone this trip any more.

Problem is Air Canada uses the 777w configuration for this flight and so it's 3x3x3 seat configuration. So we won't be able to have 4 seats and be able to sit together.

If the flight is not full, would we be able to ask the flight staff for another seat elsewhere on the plane so that the kids can stretch out in 2 seats with one of us, while the other seats elsewhere?