In regards to your first question about the practice exams, you need to follow the instructions in your book.
Step one: log onto to the website indicated in your book
Step two: in the top right corner click on the "Register Now tab"
Step three: register yourself with a user name and password
As for your second question simply logon to www.adcaonline.org and select the membership tab add two memberships to your cart, then go to the certification tab add two certification exams upon checkout there is a (NOTES) area simply put the names of the persons you want along with their e-mail address and it will be manually inputed into the system (example: These memberships and exams are for Jane Doe- jane@email.com and John Doe - John @email.com) If you have any further questions please contact technical support at support@adcaonline.org