Train Ticket Office at T2, PEK

Dear Sir/Madam,
Kindly asking to ensure. This site mentioned that there is Train Ticket Office at T2.
1.Does this office sell bullet train ticket from Bejing to Xi'an, too ?
2. How about the price, higher than if we buy online or buy at the West Station
3. Is there similar train ticket office at T3?
4. I will be arrive at T3 , IF train ticket office not available at T3, is it allowed for me to enter at T2 to buy this ticket?

Please kindly advise.

Thankyou & Regards,
Dwira