Aircraft are pressurized to the equivalent of 8000 above sea level, and this cuts down quite a bit on the partial pressure of oxygen you breath, although it is still 21% of the total. I skydive, and have done quite a few night freefalls, and we are trained that at 8000ft there is effectively half the oxygen at sea level in the lungs. At that point our night vision starts to disappear.
If the boys aren't oxygen starved now on the ground, they will probably be all right in the air. A test will spot any tendency to get hypoxic on a lower oxygen partial press. My young cf friend needs O2 all the time, and I am trying to figure out a concentrator to take her on a plane ride, one that will get past the TSA. No point in trying to carry a tank past them, looks like a weapon of mass destruction...