between zhangbi castle & Wang's courtyard house in Pingyao; & train ticket service

Hello,
First, I'd like to let you know that I appreciate this website. It provides a lot of content that i can't found on others. so let me ask some questions:
1. if one will be chosen; outside of Pingyao, which one will you choose between zhangbi underground castle & Wang Family courtyard house?
2. Is zhangbi castle suitable for my dad; 70-year-old without underlying disease, and, he can walk well in general? Coz i've heard that it's quite difficult to walk due to the rough walkway.
3. Can I book the whole-trip train tickets on one day? such as, when I'm in Xian, can I book the trains bound for Datong from Pingyao & from Datong to Beijing or I need to be at each station to book for it?
Thanks for your kindness. If there's any mistake about my English, I apologized.