Transit visa required, I am Belgian passport holder?

Hello,

my parents booked a flight to New Zealand, They are Belgian passport holders, and this is there flight schedule :
Amsterdam - Bejing
Bejing - Guangzhou (national flight in china)
Guangzhou - Auckland

They are no longer than 11 hours in China.

When they return they have the next schedule :
Aucklan - Guangzou
Guangzou - Chengdu
Chengdu - Amsterdam

They are no longer than 9 hours in China

Nobody seems to give us a certain answer. Do they need a transit-visa or not. They all say : "normally not but it's better to get one --> price 250€". I rather would know for sure though :-)

Thanks in advance!

Regards