Hi, Mrs. Geller.
There is no direct train from Tianjin to Shantou. You need to connect a train via Guangzhou or Shenzhen. I think Shenzhen is better. From Tianjin to Shenzhen, it takes about 33 hours. A lower soft sleeper costs 720RMB and upper one costs 690RMB. Then from Shenzhen to Shantou, you have to spend more than 8 hours on the train. 224RMB for a lower soft sleeper and 215RMB for upper one.

No direct train from Shantou to Shanghai as well. Take Guangzhou or Shenzhen as a connection station. And you need to stay ovenight there. Why don't you fly to Shanghai from Shantou directly?