The Complete NGC Gaming Event is only for Visitors older than 16 years accessible. The LAN Area is is only for visitors older then 18 years accessible. Please consider this regarding your plans (as well as for your teammates and friends).
There is no grey zone in this topic. There's no exception rule for brothers and sisters or children of adult visitors. Even if the regulatory obligation is accepted by one of these adults. In this case the German Youth Protection is very strict. E.g. visitors which have their 18th birthday at saturday are only allowed to enter the LAN-Area at this day 0:00 AM.
Please dont forget to bring your ID-Card as a verification of your age.