I'm not from the US, and neither are the people we're talking about. These people look like they weigh less than 88 kilograms, which I agree would be obese for 176cm.
Oh I wasn't aware that there were testable definitions. Then I consider it unlikely that the adults in the German family are either obese or overweight. On what are you basing your claim that their BMI is greater than 25 kgm^-2?
Also BMI is getting phased out in favour of ratio between circumferences of hips and belly. It has much better correlation with lots of diseases than BMI.
Obese: http://en.wikipedia.org/wiki/Obesity
Overweight: http://en.wikipedia.org/wiki/Overweight