buy train tickets through TravelChinaguide from Beijing to Datong and from Datong to Xian

I would like to buy train tickets through TravelChinaguide from Beijing to Datong and from Datong to Xian. Am I sure to have the tickets if I buy them in time? May I receive the two tickets in my hotel in Beijing or will I receive the first one in Beijing and the second one in Datong? I won't have the time to buy the tickets in either town. If I'm not sure to be able to buy them in advance, I have to change my plans. Thank you for your answer.