As mentioned in my post, #4 was not their fault. Sorry for not mentioning the effect of number 3, but it is actually quite relevant - that caused a 10 to 15 minute delay; the Japanese officials had to recreate the ticket after verifying that indeed my wife's name is the one that was booked. If poor service is the norm in the industry, then I would agree with you that only #2 is AC's fault, but I have higher standards. Here's what should have happened:

1) the counter lady should have told us, "make sure you report directly to the gate as I was not able to get seats for you".
2) the counter lady should have NOT told us, "you do NOT need to pick up your checked-in bags in Tokyo"
3) the counter lady should have entered my wife as an adult. As a software developer who has worked with enterprise systems requiring databases, there should have been a consistency check in their system which would have prevented what happened - my wife was an Adult from Vancouver to Tokyo and then became a Child from Tokyo to Nagoya
4) when they realized that we were booked in separate seats, according to the stewardess' apology to us (which we appreciated) and as you mentioned, they should have been able to seat us together
5) when they saw that my son could barely stand, they should have offered a wheelchair
6) since I did not ask for any compensation when I emailed them about my complaints, instead of sending an insincere compensation, they should not have sent any compensation at all; again, as I mentioned, they regularly give out "15% off" their published web fares; in fact, I just got an email sent to everyone in their email list for 15% off just 4 days ago