hi Jessie, I suggest you four have one compartment in the soft sleeper train carriage from Qingdao to Xian, which is much comfortable. One compartment costs you about CNY2070 in total.

In the hard sleeper comparment, there is six berths. Two upper berths, two middle berths and two lower berths in one compartment. The upper berth costs CNY324 per person, middle one costs CNY335 per person and the lower one costs CNY345 per person.

From Guilin to Hangzhou, one soft sleeper compartment is CNY2002 in total. And the hard sleeper tickets cost as following:
upper berth CNY312
middle berth CNY323
lower berth CNY333