Multi stops in Beijing and Shanghai

Hello, we are a family of 4 travelling from Vancouver to Shanghai, less than 72 hours in the city, then fly to the Phillipines, for 2 weeks. We will fly back into Beijing, visit the Great Wall hopefully, and then take a train back to Shanghai to fly back to Canada, again less than 72 hours in China but for a second time. Do we need a visa, do I need to apply for two separate ones for each arrival in China, and if yes to Visa, what kind? Thank you kindly