Hi My husband and I like to visit Yan'an and Hu Kou Fall.

It is fine to go via Xian or YA.
Direct bullet trains to YA are available from Xian North Station only take around 2h. Upon arriving, opposite the railway station is the South Bus Station, where there are direct buses to the waterfall. If departing from Xian directly to the fall, at the Fangzhicheng Bus Station, there are two direct buses leaving at 08:00 and 13:20. The travel time is about 5 hours. I also remember there is only one direct bus from Chengbei Bus Station, departing at 12:00.