^ the lesson learned is not just check your travel documents but check the country-specific requirements. Also, this being the first time I've had to renew US passports I was shocked that the US requires you to hand in your passport - and thus be totally unable to travel - while applying for a new one. It was really that last requirement that nailed us and caused the trouble with timing.
Also agree that it is beyond idiotic to forge anything to do with immigration requirements. That's a really fast way to land yourself in custody and potentially be banned from visiting a country for life. I've spent some time being interrogated by immigration officials and had my passport seized. It's not a pleasant experience for an adult and would be triply awful with children. (I was in the right but that didn't give me any rights or speed things up - I just had to go through the process, be polite and keep pointing at my totally okay documentation and how I was 100% conforming with the constraints on my visas etc). An expired passport is small beans in comparison.
Thanks again for all the advice.
baobab