Is it possible to order online tickets and pick them at the entrance of the Shaanxi History Museum?

Yes, you can reserve the ticket at the official website online, and then collect the ticket on the spot. The reservation system only has Chinese versions, so you may ask your Chinese friends or hotel staff for help. The ticket of the Exhibition Hall for Mural Paintings of Tang Dynasty can also be booked online.

From North Gate of City Wall, you can take bus line 26 from North Gate Station to Cuihua Road, Eastern End of East Xiaozhai Road Station. Then, you can see it. Or, you can taxi there for about CNY 20. :)

Thanks a lot, Jacob.
I found the ticket reservation on the museum website by using google translate :-).
Thanks also for the bus line.

One more question.
I will visit the museum together with my daughter (10yo, 1.4m). Should I make two account, or can I reserve two tickets with one account?
Thank you.

One account can book one ticket each day. So, you should open two accounts. :)

Thanks a million, Jacob!