144-Visa-free trip to Beijing possible? Travel plan: Germany->Hongkong->Beijing->Germany

My friends want to visit me in Beijing(I work here at the moment). And they try to avoid to apply for a visa. The master plan is to fly from Frankfurt to Hongkong. We want to meet us there. Then for 6 days to Beijing and back to Germany. Is this order in the travel plan OK? Or do they have to fly at first to BJ and then via HK back to Germany?

Thanks in advance for your answer(s)