Chinese people's names consist of a surname and a given name. The surname comes first, followed by the given name. But in translations, when Chinese names are translated, we like to reverse the order so westerners can figure out the surname easily. So in Jenny's chase, her Chinese name in normal order is Chen Qun Dan, Chen being her surname, ie. family name, and Qun Dan being her given name. In my translation I reversed the order for the reason mentioned above. Her brother's name is Chen Qun Yu. They share the same surname Chen, obviously. And it is very common for siblings to share a common characters in their given names. In this chase, the common character is Qun.
I hope this clears things up!