I'm planning to travel to Beijing, Nanjing and Tonxiang

Hi, firstly, do you mean Tongxiang of Zhejiang? If so, here is my suggestion. Actually, during the journey, train is suggested. You may take a flight from your country to Beijing. So you can start your trip from Beijing where there are many attractions. After traveling in Beijing, you can take a direct train to Nanjing at Beijing South Railway Station. Then you can also choose to take a train to Tongxiang upon the end of your Nanjing traveling. And after the Tongxiang trip, the direct train from Tongxiang can take you back to Beijing. Anyway, there is only one train on schedule from Tongixang to Beijing each day, departing at 08:05.
May the information help, good luck!