How do you visit Beijing,Xian,chengdu,Gullin & Hongkong with family of 4 going by train and flight?

I happened to travel the same journey last Nov. but I also traveled to Shanghai.
Anyway, here is my suggestion:
BJ to Xian, it is highly recommended to take the high-speed train, which takes about 4.5h. After visiting Xian, Chengdu can be followed and can be reached by train (about 15 hours travel journey) or by air (about 1 hour and 15 min).
Afterwards, you can fly from Chengdu to Guilin. Then the travel from Guilin to HK is also suggested to take a plane.