Additional customer's info

-- url of the page with the problem -- : www.be4eat.com/be4eat2016-biglietto
-- Joomla version -- : 3.3.3

Hi, I create product to sell tickets for our congress.
Now if a customer buy one ticket, he can insert his information and so no problem!
I would be that if customer buy 2 tickets or 3 tickets ... hikashop automatically ask data (name, surname, email, mobile, etc.) information about 2nd or 3nd partecipant.
I don't want to insert several fields if are not needed.
This is my page: www.be4eat.com/be4eat2016-biglietto
How can I resolve this problem?