I am planning a trip that will include several train legs, Beijing to Pingyao. Pingyao to Xian, Xian to Louyang and then onto to Shanghai either by train or plane. There will be 3 of us traveling together, if we book soft sleeper accommodations for 3 are we likely to have a 4th person in our compartment?

Also, what is the best way to book all these legs, should they be booked before we go to Beijing? We will be leaving Beijing around May 3 or 4 of 2011.
Many thanks to anyone with advice.