United States -- Beijing -- Hong Kong -- then cruise to Vietnam, Cambodia, Thailand, Singapore

My family of five U.S. citizens with valid passports is traveling U.S. -- Beijing -- Hong Kong -- then cruise to Vietnam, Cambodia, Thailand, and Singapore. We will be in Beijing for approx. 48 hours and have e-ticket confirmation for a flight on Air China to Hong Kong. After 3 days in Hong Kong, our ship leaves and heads to Vietnam and the rest. Can we use the 72-hour Visa-free transit in Beijing? Thank you in advance for your advice.