We want to go from Beijing to Hong Kong

What train do we take to go from Beijing to Hong Kong. We will be staying at the Doubletree by Hilton Hotel. We have a cruise departing from Hong Kong and want to take the train. We're concerned about the timeline, immigration and so forth. We can depart from Beijing on the 16th our cruise leaves on the 20th. Where does the rail arrive in Hong Kong in relationship to the docks for the cruises. (We'll be looking for a place to stay there prior to the it, as well.) Thanks for your time.